TCP retransmission and exception processing in high speed, low memory hardware devices

ABSTRACT

A method and system for the retransmission of TCP segments in a high speed, low memory TOE device or processor system uses one or more selective context duplication (SCD) TCP/IP connections to provide retransmission assistance to an original TCP/IP connection. SCD connections are used only to retransmit TCP segments on behalf of the system. The original connection and SCD connections are linked together and managed using a TCP state engine in such a way that the original connection receives and processes acknowledgements (ACKs) and selective acknowledgements (SACKs) transmitted back to the system. In many applications, the original connection is able to continue transmitting even while the SCD connection is retransmitting.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.provisional patent application No. 60/583,310, entitled “TOE METHODS ANDSYSTEMS,” filed Jun. 28, 2004, which is incorporated herein in itsentirety by reference.

FIELD OF THE PRESENT INVENTION

The present invention relates generally to computer communicationsystems and protocols, and, more particularly, to methods and systemsfor TCP retransmission and exception processing in high speed, lowmemory TCP dedicated hardware devices.

BACKGROUND OF THE PRESENT INVENTION

TCP/IP is a protocol system—a collection of protocols, rules, andrequirements that enable computer network communications. At its core,TCP/IP provides one of several universally-accepted structures forenabling information or data to be transferred and understood (e.g.,packaged and unpackaged) between different computers that communicateover a network, such as a local area network (LAN), a wide area network(WAN), or a public-wide network, such as the Internet.

The “IP” part of the TCP/IP protocol stands for “Internet protocol” andis used to ensure that information or data is addressed, delivered, androuted to the appropriate entity, network, or computer system. Incontrast, “TCP,” which stands for “transport control protocol,” ensuresthat the actual content of the information or data that is transmittedis received completely and accurately. To ensure such reliability, TCPuses extensive error control and flow control techniques. Thereliability provided by TCP, however, comes at a cost—increased networktraffic and slower delivery speeds—especially when contrasted with lessreliable but faster protocols, such as UDP (“user datagram protocol”).

A typical network 100 a is illustrated in FIG. 1A and includes at leasttwo remote machines in communication with each other over acommunications medium. Specifically, as shown, one machine 110 is asending computer, server, or system (which we will arbitrarily designateas the “source machine” or TCP processor system) that communicates overa communications medium or network, such as the Internet 150, withanother machine 160, which is the receiving computer, server, or system(which we will arbitrarily designate as the “destination machine” or TCPreceiver system). Data or information typically travels in bothdirections 120, 130 between the source machine 110 and the destinationmachine 160 as part of a normal electronic communication.

In more complex computer networks, such as network 100 b as illustratedin FIG. 1B, one server 115 acts as a source machine on behalf ofnumerous computers 111 networked with the server 115 that communicateover the communications medium or network 150, with other servers 165,each with their own networked computers 185,186,187. Server 115 alsocommunicates with other standalone computers 175. Data or informationtypically travels in both directions on communication lines 125 betweensource machines and destination machines as part of normal electroniccommunications.

It is helpful to understand that the TCP/IP protocol defines discretefunctions that are to be performed by compliant systems at different“layers” of the TCP/IP model. As shown in FIG. 2, the TCP/IP model 200includes four layers, namely, the network access layer 210, the internetlayer 220, the transport layer 230, and the application layer 240. Eachlayer is intended to be independent of the other layers, with each layerbeing responsible for different aspects of the communication process.For example, the network access layer 210 provides a physical interfacewith the physical network and formats data for the transmission medium,addresses data based on physical hardware addresses, and provides errorcontrol for data delivered on the physical network. Among other things,the internet layer 220 provides logical, hardware-independent addressingto enable data to pass between systems with different architectures. Thetransport layer 230 provides flow control, error control, andacknowledgment services, and serves as an interface for networkapplications. The application layer 240 provides computer applicationsfor network troubleshooting, file transfer, remote control, and Internetactivities.

According to TCP/IP protocol, each layer plays its own role in thecommunications process. For example, out-going data from the sourcemachine is packaged first at the application layer 240, and then it ispassed down the stack for additional packaging at the transport layer230, the internet layer 220, and then finally the network access layer210 of the source machine before it is transmitted to the destinationmachine. Each layer adds its own header (and/or trailer) information tothe data package received from the previous higher layer that will bereadable and understood by the corresponding layer of the destinationmachine. Thus, in-coming data received by a destination machine isunpackaged in the reverse direction (from network access layer 210 toapplication layer 240), with each corresponding header (and/or trailer)being read and removed from the data package by the respective layerprior to being passed up to the next layer.

The process 300 of encapsulating data at each successive layer isillustrated briefly in FIG. 3. For example, out-going user data 305 ispackaged by a computer application 341 to include application header345. The data package 340 created by the application 341 is called a“message.” The message 340 (also shown as application data 342) isfurther encapsulated by a TCP manager 331 to include TCP header 335(note: for purposes of the present invention and discussion, thetransport layer is TCP rather than another protocol, such as UDP). Thedata package 330 created by the TCP manager 331 is called a “segment”The segment 330 is encapsulated further by the IP manager 321 to includeIP header 325. The data package 320 created by the IP manager 321 iscalled a “datagram.” The datagram 320 is encapsulated yet further by anEthernet driver 311 (at the network access layer) to include Ethernetheader 315 and Ethernet trailer 316. The data package 310 created by theEthernet driver 311 is called a “frame.” This frame 310 is a bitstreamof information that is transmitted, as shown in FIG. 1, across thecommunications medium 150 from the source machine 110 to the destinationmachine 160. As stated previously, the process at the destinationmachine 160 of unpacking each data package occurs. by layer, in thereverse order.

It should be understood that the amount of data that needs to betransmitted between machines often exceeds the amount of space that isfeasible, efficient, or permitted by universally-accepted protocols fora single frame or segment. Thus, data to be transmitted and receivedwill typically be divided into a plurality of frames (at the IP layer)and into a plurality of segments (at the TCP layer). TCP protocolsprovide for the sending and receipt of variable-length segments ofinformation enclosed in datagrams. TCP protocols provide for the properhandling (transmission, receipt, acknowledgement, and retransmission) ofsegments associated with a given communication.

At its lowest level, computer communications of data packages or packetsof data are assumed to be unreliable. For example, packets of data maybe lost or destroyed due to transmission errors, hardware failure orpower interruption, network congestion, and many other factors. Thus,the TCP protocols provide a system in which to handle the transmissionand receipt of data packets in such an unreliable environment. Forexample, based on TCP protocol, a destination machine is adapted toreceive and properly order segments, regardless of the order in whichthey are received, regardless of delays in receipt, and regardless ofreceipt of duplicate data. This is achieved by assigning sequencenumbers (left edge and right edge) to each segment transmitted andreceived. The destination machine further acknowledges correctlyreceived data with an acknowledgment (“ACK”) or a selectiveacknowledgment (“SACK”) back to the source machine. An ACK is a positiveacknowledgment of data up through a particular sequence number. Byprotocol, an ACK of a particular sequence number means that all data upto but not including the sequence number ACKed has been received. Incontrast, a SACK, which is an optional TCP protocol that not all systemsare required to use, is a positive acknowledgement of data up through aparticular sequence number, as well as a positive acknowledgment of upto 3-4 “regions” of non-continguous segments of data (as designated bytheir respective sequence number ranges). From a SACK, a source machinecan determine which segments of data have been lost or not yet receivedby the destination machine. The destination machine also advertises its“local” offer window size (i.e., a “remote” offer window size from theperspective of the source machine), which is the amount of data (inbytes) that the destination machine is able to accept from the sourcemachine (and that the source machine can send) prior to receipt of(i.e., without having to wait for) any ACKs or SACKs back from thedestination machine. Correspondingly, based on TCP protocols, a sourcemachine is adapted to transmit segments of data to a destination machineup to the offer window size advertised by the destination machine.Further, the source machine is adapted to retransmit any segment(s) ofdata that have not been ACKed or SACKed by the destination machine.Other features and aspects of TCP protocols will be understood by thoseskilled in the art and will be explained in greater detail only asnecessary to understand and appreciate the present invention. Suchprotocols are described in greater detail in a number ofpublicly-available RFCs, including RFCs 793, 2988, 1323, and 2018, whichare incorporated herein by reference in their entirety.

The act of formatting and processing TCP communications at the segmentlevel is generally handled by computer hardware and software at each endof a particular communication. Typically, software accessed by thecentral processing unit (CPU) of the sender and the receiver,respectively, manages the bulk of TCP processing in accordance withindustry-accepted TCP protocols. However, as the demand for the transferof greater amounts of information at faster speeds has increased and asavailable bandwidth for transferring data has increased, CPUs have beenforced to devote more processing time and power to the handling of TCPtasks—at the expense of other processes the CPU could be handling. “TCPOffload Engines” or TOEs, as they are often called, have been developedto relieve CPUs of handling TCP communications and tasks. TOEs aretypically implemented as network adapter cards or as components on anetwork adapter card, which free up CPUs in the same system to handleother computing and processing tasks, which, in turn, speeds up theentire network. In other words, TCP tasks are “off-loaded” from the CPUto the TOE to improve the efficiency and speed of the network thatemployees such TOEs.

Conventional TOEs use a combination of hardware and software to handleTCP tasks. For example, TOE network adapter cards have software andmemory installed thereon for processing TCP tasks. TOE applicationspecific integrated circuits (ASICs) are also used for improvedperformance; however, ASICs typically handle TCP tasks usingfirmware/software installed on the chip and by relying upon and makinguse of readily-available external memory. Using such firmware andexternal memory necessarily limits the number of connections that can behandled simultaneously and imposes processing speed limitations due totransfer rates between separate components. Using state machinesdesigned into the ASIC and relying upon the limited memory capabilitythat can be integrated directed into an ASIC improves speed, but raisesa number of additional TCP task management hurdles and complications ifa large number of simultaneous connections are going to be managedefficiently and with superior speed characteristics.

For these and many other reasons, there is a need for systems andmethods for improving TCP processing capabilities and speed, whetherimplemented in a TOE or a CPU environment.

There is a need for systems and methods of improving the speed of TCPcommunications, without sacrificing the reliability provided by TCP.

There is a need for systems and methods that take advantage of statemachine efficiency for handling TCP tasks but in a way that remainscompliant and compatible with conventional TCP systems and protocols.

There is a need for systems and methods that enable state machineimplemented on one or more computer chips to handle TCP communicationson the order of 1000 s and 10,000 s simultaneous communications and atprocessing speed exceeding 10 GHz.

There is a need for a system using a hardware TOE device that is adaptedto support the Selective ACK (SACK) option of TCP protocol so that asource machine is able to cut back or minimize unnecessaryretransmission. In other words, a system in which the source machineonly retransmits the missing segments and avoids or minimizes heavynetwork traffic.

There is a need for systems and methods of continuing transmission ofTCP segments for a particular communication even while simultaneouslyretransmitting TCP segments for the same communication.

There is a need for systems and methods of retransmitting TCP segmentsusing a TCP state machine with limited on-chip memory.

There is a need for a system for efficiently retransmitting one or moreTCP segments in a fast retransmission arrangement when SACK tracking isnot being used.

There is a need for a system for efficiently retransmitting one or moreTCP segments in a fast retransmission arrangement when SACK tracking isenabled and when such retransmission includes TCP segments between alast ACKed segment and a SACK region or between two SACK regions.

There is a need for a system for efficiently retransmitting TCP segmentsafter a retransmission time out (RTO) condition in which no ACKs arereceived back from the TCP receiver system after a predetermined windowof time.

There is a need for a system having an improved TCP window calculatoradapted for use in a high speed, low memory hardware TOE device.

For these and many other reasons, there is a general need for a systemor method for the retransmission of a TCP segment to a TCP receivingsystem in a processor system for the management of TCP communicationswherein the processing system manages an original TCP connection with aTCP receiving system, the original TCP connection having socket,transmission, and reception characteristics and wherein the methodcomprises the steps of determining that the TCP segment previouslytransmitted on the original TCP connection to the TCP receiving systemneeds to be retransmitted and further establishing a selective contextduplicated connection with the TCP receiving system, the selectivecontext duplicated connection distinct from but having similar socketand transmission characteristics as the original TCP connection. Themethod further provides for retransmitting the TCP segment to the TCPreceiving system by using the selective context duplicated connectionrather than the original TCP connection and subsequently maintaining theoriginal TCP connection for on-going transmission of additional TCPsegments to the TCP receiving system and for receipt of communicationsback from the TCP receiving system responsive to the TCP segmentretransmitted on the selective context duplicated connection.

There is also a general need for a system or method for theretransmission of a TCP segment to a designated one of a plurality TCPreceiving systems in a processing system for the management of TCPcommunications, wherein the processor system is in electroniccommunication with the plurality of TCP receiving systems and whereinthe method comprises the steps of managing a plurality of original TCPconnections with the plurality of TCP receiving systems, each originalTCP connection having respective socket, transmission, and receptioncharacteristics. The method also determines that the TCP segmentpreviously transmitted to the designated one TCP receiving system on theoriginal TCP connection with the designated one TCP receiving systemneeds to be retransmitted, in addition to establishing a selectivecontext duplicated connection with the designated one TCP receivingsystem, the selective context duplicated connection distinct from buthaving similar socket and transmission characteristics as the originalTCP connection with the designated one TCP receiving system. The TCPsegment is retransmitted to the receiving TCP system using the selectivecontext duplicated connection rather than the original TCP connectionwith the designated one TCP receiving system. Further the original TCPconnection is maintained with the designated one TCP receiving systemfor on-going transmission of additional TCP segments to the designatedone receiving TCP system and for receipt of communications back from thedesignated one receiving TCP system responsive to the TCP segmentretransmitted on the selective context duplicated connection.

There is also a general need, in a TCP fast retransmit communicationsystem having a TCP transmitter system in communication with a pluralityof TCP receiving systems, for a system or method having a TCPtransmitter system that comprises a plurality of available connectionswherein the available connections include a plurality of original TCPconnections and at least one connection available as a selective contextduplicated connection. Additionally, a TCP state engine is configured tomaintain the plurality of original TCP connections and to transmit TCPsegments over the plurality of original TCP connections to each of theplurality of TCP receiving systems and to receive acknowledgements ofreceived TCP segments back from each of the TCP receiving systems, eachoriginal TCP connection having respective socket, transmission, andreception characteristics, a TCP micro engine in electroniccommunication with the TCP state engine, the TCP micro engine configuredto establish the selective context duplicated connection between the TCPstate engine and a designated one TCP receiving system upon receipt of aretransmission assistance request by the TCP state engine. Further,wherein after determination by the TCP state engine that a particularTCP segment has not been acknowledged by the designated one TCPreceiving system, the TCP state engine transmits the retransmissionassistance request to the TCP micro engine to establish the selectivecontext duplicated connection with the designated one TCP receivingsystem, the particular TCP segment being retransmitted to the designatedone TCP receiving system on the selective context duplicated connectionrather than on the original TCP connection with the designated one TCPreceiving system, the selective context duplicated connection distinctfrom but having similar socket and transmission characteristics as theoriginal TCP connection with the designated one TCP receiving system.

There is also a general need, in a processor system for managing TCPcommunications, the processor system managing an original TCP connectionwith a TCP receiving system, the original TCP connection having socket,transmission, and reception characteristics, for a system or method forthe fast retransmission of one or more contiguous TCP segments precedinga SACK region of TCP segments comprising the steps of determining thatthe one or more contiguous TCP segments previously transmitted on theoriginal connection to the TCP receiving system needs to beretransmitted and as a result establishing a selective contextduplicated connection with the TCP receiving system, the selectivecontext duplicated connection having similar socket and transmissioncharacteristics as the original TCP connection. Further, the methodcomprises the steps of retransmitting the one or more contiguous TCPsegments to the TCP receiving system using the selective contextduplicated connection and maintaining the original TCP connection foron-going transmission of additional TCP segments to the TCP receivingsystem and for receipt of communications back from the TCP receivingsystem responsive to the one or more contiguous TCP segmentsretransmitted on the selective context duplicated connection.

There is also a general need, in a processor system for managing TCPcommunications, the processor system managing an original TCP connectionwith a TCP receiving system, the original TCP connection having socket,transmission, and reception characteristics, a system or method for thefast retransmission of one or more contiguous TCP segments comprisingthe steps of determining that the one or more contiguous TCP segmentspreviously transmitted on the original TCP connection to the TCPreceiving system need to be retransmitted, the one or more contiguousTCP segments located between first and second SACK regions of TCPsegments and establishing a selective context duplicated connection withthe TCP receiving system, the selective context duplicated connectionhaving similar socket and transmission characteristics as the originalTCP connection. The method further retransmits the one or morecontiguous TCP segments to the TCP receiving system using the selectivecontext duplicated connection and maintains the original TCP connectionfor on-going transmission of additional TCP segments to the TCPreceiving system and for receipt of communications back from the TCPreceiving system responsive to the one or more contiguous TCP segmentsretransmitted on the selective context duplicated connection.

There is also a general need for a processor system for managing TCPcommunications, the processor system managing an original TCP connectionwith a TCP receiving system, the original TCP connection having socket,transmission, and reception characteristics, that comprises a method forthe fast retransmission of first and second groups of one or morecontiguous TCP segments, comprising the steps of determining that thefirst and second groups of one or more contiguous TCP segmentspreviously transmitted on the original TCP connection to the TCPreceiving system need to be retransmitted, the first group of one ormore contiguous TCP segments preceding a first SACK region of TCPsegments, the second group of one or more contiguous TCP segmentslocated between the first SACK region and a second SACK region of TCPsegments; establishing a selective context duplicated connection withthe TCP receiving system, the selective context duplicated connectionhaving similar socket and transmission characteristics as the originalTCP connection. The method further retransmits the first and secondgroups of one or more contiguous TCP segments to the TCP receivingsystem using the selective context duplicated connection; andmaintaining the original TCP connection for on-going transmission ofadditional TCP segments to the TCP receiving system and for receipt ofcommunications back from the TCP receiving system responsive to thefirst and second groups of one or more contiguous TCP segmentsretransmitted on the selective context duplicated connection.

There is also a general need, in a processor system for managing TCPcommunications, the processor system managing an original TCP connectionwith a TCP receiving system, the original TCP connection having socket,transmission, and reception characteristics, for a system or method forthe fast retransmission of first and second groups of one or morecontiguous TCP segments comprising the steps of determining that thefirst group of one or more contiguous TCP segments previouslytransmitted on the original TCP connection to the TCP receiving systemneed to be retransmitted, the first group preceding a first SACK regionof TCP segments and establishing a first selective context duplicatedconnection with the TCP receiving system, the first selective contextduplicated connection having similar socket and transmissioncharacteristics as the original TCP connection. The method furtherretransmits the first group of one or more contiguous TCP segments tothe TCP receiving system using the first selective context duplicatedconnection and determines that the second group of one or morecontiguous TCP segments previously transmitted on the original TCPconnection to the TCP receiving system need to be retransmitted, thesecond group located between the first SACK region and a second SACKregion of TCP segments; establishing a second selective contextduplicated connection with the TCP receiving system, the secondselective context duplicated connection also having similar socket andtransmission characteristics as the original TCP connection. Next, themethod retransmits the second group of one or more contiguous TCPsegments to the TCP receiving system using the second selective contextduplicated connection and maintains the original TCP connection foron-going transmission of additional TCP segments to the TCP receivingsystem and for receipt of communications back from the TCP receivingsystem responsive to the first and second groups of one or morecontiguous TCP segments retransmitted on the first and second selectivecontext duplicated connections.

The present invention meets one or more of the above-referenced needs asdescribed herein in greater detail.

SUMMARY OF THE PRESENT INVENTION

The present invention relates generally to computer communicationsystems and protocols, and, more particularly, to methods and systemsfor high speed TCP communications using improved TCP Offload Engine(TOE) techniques and configurations. Briefly described, aspects of thepresent invention include the following.

A first aspect of the present invention is directed to a method for theretransmission of a TCP segment to a TCP receiving system in a processorsystem for the management of TCP communications wherein the processingsystem manages an original TCP connection with a TCP receiving system,the original TCP connection having socket, transmission, and receptioncharacteristics. The method comprises the steps of determining that theTCP segment previously transmitted on the original TCP connection to theTCP receiving system needs to be retransmitted and further establishinga selective context duplicated connection with the TCP receiving system,the selective context duplicated connection distinct from but havingsimilar socket and transmission characteristics as the original TCPconnection. The method further provides for retransmitting the TCPsegment to the TCP receiving system by using the selective contextduplicated connection rather than the original TCP connection andsubsequently maintaining the original TCP connection for on-goingtransmission of additional TCP segments to the TCP receiving system andfor receipt of communications back from the TCP receiving systemresponsive to the TCP segment retransmitted on the selective contextduplicated connection.

In a feature of this first aspect of the invention the step ofdetermining is responsive to a timeout condition without receipt of anacknowledgement (ACK) from the TCP receiving system for the TCP segmentpreviously transmitted by the processor system. Further features of thepresent invention provide that no further TCP segments are transmittedby the processor system until an acknowledgment of the retransmitted TCPsegment is received back from the TCP receiving system and the selectivecontext duplicated connection is closed as soon as the TCP segment isretransmitted to the TCP receiving system. Additionally, theretransmission is a fast retransmission and the original TCP connectionis maintained for receipt of an acknowledgement (ACK) back from the TCPreceiving system responsive to the TCP segments retransmitted on theoriginal TCP connection.

In additional features of the present aspect of the invention the stepof determining is responsive to the receipt by the processor system ofthree duplicate acknowledgements (ACKs) from the TCP receiving system,wherein the TCP segment that needs to be retransmitted comprises thesegment having a left edge sequence number corresponding to the sequencenumber of the three duplicate ACKs. Further, the receptioncharacteristics of the selective context duplicated connection aredisabled and the reception characteristics of the original TCPconnection are not used to define the selective context duplicatedconnection. Also, the selective context duplicated connection does notreceive any communications back from the TCP receiving system and theoriginal TCP connection and the selective context duplicated connectionare linked together by means of a TCP micro engine.

In a yet further feature of the present aspect the step of determiningcomprises identifying a time out condition associated with the originalTCP connection, further, wherein the TCP segment that needs to beretransmitted comprises the segment having a left edge sequence numbercorresponding to the sequence number of ACK last received from the TCPreceiving system. Also, a feature of the present invention furthercomprises the step of calculating a new RTO timer for the TCP segmentthat is retransmitted using the selective context duplicated connectionand loading the value of the RTO timer to the original TCP connection.Further, the on-going transmission of additional TCP segments to the TCPreceiving system using the original TCP connection occurscontemporaneously with the step of retransmitting the TCP segment to theTCP receiving system using the selective context duplicated connectionand the processor system includes a TCP state machine and a TCP microengine.

In another feature of the first aspect of the invention the step ofestablishing the selective context duplicated connection with the TCPreceiving system is performed by the TCP micro engine after receipt of aretransmission assistance request from the TCP state engine, wherein theselective context duplicated connection is closed by the TCP microengine as soon as the TCP segment is retransmitted to the TCP receivingsystem by the TCP state machine. Additionally, the selective contextduplicated connection is closed as soon as the TCP segment isretransmitted to the TCP receiving system. When the selective contextduplicated connection is closed, the socket and transmissioncharacteristics of the selective context duplicated connection are resetand the selective context duplicated connection is made available to theprocessor system for retransmission use with another original TCPconnection.

In yet further features of the present aspect of the invention thesequence number of the last received ACK of the original TCP connectionis used to define the left edge sequence number of the TCP segment to beretransmitted and further comprised is a step of creating a data linklist for the selective context duplicated connection with pointerspointing to data that needs to be retransmitted. Also, the data thatneeds to be retransmitted is included in the TCP segment that isretransmitted, wherein after determining that the TCP segment needs tobe retransmitted, calculating a congestion window size for the originalTCP connection and the selective context duplicated connection isunaffected by the congestion window size of the original TCP connection.

Another aspect of the present invention is directed to a method for theretransmission of a TCP segment to a designated one of a plurality TCPreceiving systems in a processing system for the management of TCPcommunications, wherein the processor system is in electroniccommunication with the plurality of TCP receiving systems. The methodcomprises the steps of managing a plurality of original TCP connectionswith the plurality of TCP receiving systems, each original TCPconnection having respective socket, transmission, and receptioncharacteristics.

The method also determines that the TCP segment previously transmittedto the designated one TCP receiving system on the original TCPconnection with the designated one TCP receiving system needs to beretransmitted, in addition to establishing a selective contextduplicated connection with the designated one TCP receiving system, theselective context duplicated connection distinct from but having similarsocket and transmission characteristics as the original TCP connectionwith the designated one TCP receiving system. The TCP segment isretransmitted to the receiving TCP system using the selective contextduplicated connection rather than the original TCP connection with thedesignated one TCP receiving system. Further the original TCP connectionis maintained with the designated one TCP receiving system for on-goingtransmission of additional TCP segments to the designated one receivingTCP system and for receipt of communications back from the designatedone receiving TCP system responsive to the TCP segment retransmitted onthe selective context duplicated connection.

In a feature of the present aspect of the invention the step ofdetermining is responsive to a timeout condition without receipt of anacknowledgement (ACK) from the designated one of the TCP receivingsystems for the TCP segment previously transmitted by the processorsystem. Also, no further TCP segments are transmitted to the designatedone of the TCP receiving systems by the processor system until anacknowledgment of the retransmitted TCP segment is received back fromthe designated one of the TCP receiving systems and the selectivecontext duplicated connection is closed as soon as the TCP segment isretransmitted to the designated one of the TCP receiving systems.

In yet further features of the present aspect of the invention theretransmission is a fast retransmission and the original TCP connectionwith the designated one TCP receiving system is maintained for receiptof an acknowledgment (ACK) back from the designated one TCP receivingsystem responsive to the TCP segment retransmitted on the original TCPconnection. Additionally, the step of determining is responsive toreceipt by the processor system of three duplicate acknowledgements(ACKs) from the designated one TCP receiving system, wherein the TCPsegment that needs to be retransmitted comprises the segment having aleft edge sequence number corresponding to the sequence number of thethree duplicate ACKs.

In yet additional features of the present aspect of the invention thereception characteristics of the selective context duplicated connectionare disabled and the reception characteristics of the selective contextduplicated connection are not used to define the selective contextduplicated connection. Further, the selective context duplicatedconnection does not receive any communications back from the designatedone TCP receiving system, also the original TCP connection with thedesignated one TCP receiving system and the selective context duplicatedconnection are linked together by means of a TCP micro engine.

The step of determining comprises identifying a time out conditionassociated with the original TCP connection with the designated one TCPreceiving system in addition to the TCP segment that needs to beretransmitted comprising the segment having a left edge sequence numbercorresponding to the sequence number of ACK last received from thedesignated one TCP receiving system. Further featured is the step ofcalculating a new RTO timer for the TCP segment that is retransmitted bythe selective context duplicated connection and loading the value of theRTO timer to the original TCP connection with the designated one TCPreceiving system. The on-going transmission of additional TCP segmentsto the designated one TCP receiving system using the original TCPconnection with the designated one TCP receiving system occurscontemporaneously with the step of retransmitting the TCP segment to thedesigned one TCP receiving system using the selective context duplicatedconnection. Also, the processor system includes a TCP state machine anda TCP micro engine and the step of establishing the selective contextduplicated connection with the designed one TCP receiving system isperformed by the TCP micro engine after receipt of a retransmissionassistance request from the TCP state engine.

In yet further features of the present aspect of the invention theselective context duplicated connection is closed by the TCP microengine as soon as the TCP segment is retransmitted to the designated oneTCP receiving system by the TCP state machine and the selective contextduplicated connection is closed as soon as the TCP segment isretransmitted to the designated one TCP receiving system. Additionally,when the selective context duplicated connection is closed, the socketand transmission characteristics of the selective context duplicatedconnection are reset and the selective context duplicated connection ismade available to the processor system for retransmission use withanother original TCP connection. The sequence number of the lastreceived ACK of the original TCP connection with the designated one TCPreceiving system is used to define the left edge sequence number of theTCP segment to be retransmitted.

Another feature of the present aspect of the invention further comprisesthe step of creating a data link list for the selective contextduplicated connection with pointers pointing to data that needs to beretransmitted, wherein the data that needs to be retransmitted isincluded in the TCP segment that is retransmitted. Also, the featuresfurther comprises after determining that the TCP segment needs to beretransmitted, calculating a congestion window size for the original TCPconnection with the designated one TCP receiving system, the selectivecontext duplicated connection is unaffected by the congestion windowsize of the original TCP connection with the designated one TCPreceiving system.

In a TCP fast retransmit communication system having a TCP transmittersystem in communication over an original TCP connection with a TCPreceiving system, a further aspect of the present invention comprises aTCP transmitter system that comprises a TCP state engine that isconfigured to transmit TCP segments over the original TCP connection tothe TCP receiving system and to receive acknowledgements of received TCPsegments back from the TCP receiving system. The original TCP connectionhaving socket, transmission, and reception characteristics and a TCPmicro engine that is in electronic communication with the TCP stateengine, the TCP micro engine being configured to establish a selectivecontext duplicated connection between the TCP state engine and the TCPreceiving system upon receipt of a retransmission assistance request bythe TCP state engine. The selective context duplicated connection isdistinct from, but has similar socket and transmission characteristicsas the original TCP connection. Furthermore, wherein after adetermination by the TCP state engine that a particular TCP segment hasnot been acknowledged by the TCP receiving system, the TCP state enginetransmits the retransmission assistance request to the TCP micro engineto establish the selective context duplicated connection, the particularTCP segment being retransmitted to the TCP receiving system on theselective context duplicated connection rather than on the original TCPconnection.

In a feature of this present aspect of the invention the original TCPconnection is maintained by the TCP state engine for on-goingtransmission of additional TCP segments to the TCP receiving system andfor receipt of an acknowledgment back from the TCP receiving system uponreceipt of the particular TCP segment. Further features includeadditional TCP segments being transmitted to the TCP receiving systemusing the original TCP connection contemporaneously with theretransmission of the particular TCP segment to the TCP receiving systemusing the selective context duplicated connection and wherein thedetermination by the TCP state engine that the particular TCP segmenthas not been acknowledged by the TCP receiving system is based uponreceipt by the TCP state engine of three duplicate acknowledgements(ACKs) from the TCP receiving system.

In further features the reception characteristics of the selectivecontext duplicated connection are disabled by the TCP micro engine andthe reception characteristics of the selective context duplicatedconnection are not used to define the selective context duplicatedconnection. Also, the selective context duplicated connection is aone-way connection that does not receive any acknowledgmentcommunications back from the TCP receiving system and the originalconnection and the selective context duplicated connection are linkedtogether by the TCP micro engine. Additionally, the TCP micro enginecalculates a new RTO timer for the particular TCP segment that isretransmitted by the selective context duplicated connection andassociates the value of the RTO timer with the original TCP connection.The selective context duplicated connection is closed by the TCP microengine after the particular TCP segment is retransmitted to the TCPreceiving system, and when the selective context duplicated connectionis closed, the socket and transmission characteristics of the selectivecontext duplicated connection are reset and the selective contextduplicated connection is made available to the TCP transmitter systemfor retransmission use with another original connection.

In a TCP fast retransmit communication system having a TCP transmittersystem in communication with a plurality of TCP receiving systems, anadditional aspect of the present invention comprises a TCP transmittersystem that comprises a plurality of available connections. Theavailable connections include a plurality of original TCP connectionsand at least one connection available as a selective context duplicatedconnection. Additionally, a TCP state engine is configured to maintainthe plurality of original TCP connections and to transmit TCP segmentsover the plurality of original TCP connections to each of the pluralityof TCP receiving systems and to receive acknowledgements of received TCPsegments back from each of the TCP receiving systems, each original TCPconnection having respective socket, transmission, and receptioncharacteristics, a TCP micro engine in electronic communication with theTCP state engine, the TCP micro engine configured to establish theselective context duplicated connection between the TCP state engine anda designated one TCP receiving system upon receipt of a retransmissionassistance request by the TCP state engine. Further, wherein afterdetermination by the TCP state engine that a particular TCP segment hasnot been acknowledged by the designated one TCP receiving system, theTCP state engine transmits the retransmission assistance request to theTCP micro engine to establish the selective context duplicatedconnection with the designated one TCP receiving system, the particularTCP segment being retransmitted to the designated one TCP receivingsystem on the selective context duplicated connection rather than on theoriginal TCP connection with the designated one TCP receiving system,the selective context duplicated connection distinct from but havingsimilar socket and transmission characteristics as the original TCPconnection with the designated one TCP receiving system.

In a feature of the present aspect of the invention the original TCPconnection with the designated one TCP receiving system is maintained bythe TCP state engine for on-going transmission of additional TCPsegments to the designated one TCP receiving system and for receipt ofan acknowledgment back from the designated one TCP receiving system uponreceipt of the particular TCP segment. Further, additional TCP segmentsare transmitted to the designated one TCP receiving system using theoriginal TCP connection with the designated one TCP receiving systemcontemporaneously with the retransmission of the particular TCP segmentto the designated one TCP receiving system using the selective contextduplicated connection. The determination by the TCP state engine thatthe particular TCP segment has not been acknowledged by the designatedone TCP receiving system is based upon receipt by the TCP state engineof three duplicate acknowledgements (ACKs) from the designated one TCPreceiving system.

Additional features of the present aspect provide for the receptioncharacteristics of the selective context duplicated connection aredisabled by the TCP micro engine and the reception characteristics ofthe selective context duplicated connection are not used to define theselective context duplicated connection. Also, the selective contextduplicated connection is a one-way connection that does not receive anyacknowledgment communications back from any of the TCP receiving systemsand the original connection and the selective context duplicatedconnection with the designated one TCP receiving system are linkedtogether by the TCP micro engine.

The TCP micro engine calculates a new RTO timer for the particular TCPsegment that is retransmitted by the selective context duplicatedconnection and associates the value of the RTO timer with the originalTCP connection with the designated one TCP receiving system andadditionally the selective context duplicated connection is closed bythe TCP micro engine after the particular TCP segment is retransmittedto the designated one TCP receiving system. When the selective contextduplicated connection is closed, the socket and transmissioncharacteristics of the selective context duplicated connection are resetand the selective context duplicated connection is made available to theTCP transmitter system for retransmission use with another originalconnection.

In a processor system for managing TCP communications, the processorsystem managing an original TCP connection with a TCP receiving system,the original TCP connection having socket, transmission, and receptioncharacteristics, a yet another aspect of the present invention comprisea method for the fast retransmission of one or more contiguous TCPsegments preceding a SACK region of TCP segments. The method comprisesthe steps of determining that the one or more contiguous TCP segmentspreviously transmitted on the original connection to the TCP receivingsystem needs to be retransmitted and as a result establishing aselective context duplicated connection with the TCP receiving system,the selective context duplicated connection having similar socket andtransmission characteristics as the original TCP connection. Further,the method comprises the steps of retransmitting the one or morecontiguous TCP segments to the TCP receiving system using the selectivecontext duplicated connection and maintaining the original TCPconnection for on-going transmission of additional TCP segments to theTCP receiving system and for receipt of communications back from the TCPreceiving system responsive to the one or more contiguous TCP segmentsretransmitted on the selective context duplicated connection.

In a feature of the present aspect of the invention the step ofdetermining is responsive to receipt by the processor system of aselective acknowledgment (SACK) from the TCP receiving system, the SACKidentifying the one or more contiguous TCP segments not yet received bythe TCP receiving system that lie between a last acknowledged TCPsegment and the SACK region. Also, the one or more contiguous TCPsegments comprise a single TCP segment and the one or more contiguousTCP segments comprise a plurality of TCP segments.

In additional features of the present aspect the one or more contiguousTCP segments are defined between a left edge sequence numbercorresponding to the sequence number of the last acknowledged TCPsegment and a right edge sequence number corresponding to the sequencenumber just prior to the SACK region. Further, the receptioncharacteristics of the selective context duplicated connection aredisabled and the reception characteristics of the original TCPconnection are not used to define the selective context duplicatedconnection. Also, the original TCP connection and the selective contextduplicated connection are linked together by means of a TCP microengine.

Yet further features of the present inventive aspect comprise the stepof calculating a new RTO timer for the one or more contiguous TCPsegments that are retransmitted using the selective context duplicatedconnection and assigning the value of the RTO timer to the original TCPconnection, wherein the on-going transmission of additional TCP segmentsto the receiving TCP system using the original TCP connection occurscontemporaneously with the step of retransmitting the one or morecontiguous TCP segments to the TCP receiving system using the selectivecontext duplicated connection. Also, the processor system includes a TCPstate machine and a TCP micro engine and the step of establishing theselective context duplicated connection with the TCP receiving system isperformed by the TCP micro engine after receipt of a retransmissionassistance request from the TCP state engine.

In yet additional features of the present inventive aspect the selectivecontext duplicated connection is closed by the TCP micro engine afterthe one or more contiguous TCP segments are retransmitted to the TCPreceiving system by the TCP state machine and the selective contextduplicated connection is closed as soon as the one or more contiguousTCP segments are retransmitted to the TCP receiving system. Further, thesocket and transmission characteristics of the selective contextduplicated connection are reset and the selective context duplicatedconnection is made available to the processor system for retransmissionuse with another original TCP connection.

A yet further feature of the present inventive aspect comprises the stepof creating a data link list for the selective context duplicatedconnection with pointers pointing to data that needs to beretransmitted, wherein the data that needs to be retransmitted isincluded in the one or more contiguous TCP segments that areretransmitted. Also, the aspect further comprises the feature of afterdetermining that the one or more contiguous TCP segments need to beretransmitted, calculating a congestion window size for the original TCPconnection and the selective context duplicated connection is unaffectedby the congestion window size of the original TCP connection.

In a processor system for managing TCP communications, the processorsystem managing an original TCP connection with a TCP receiving system,the original TCP connection having socket, transmission, and receptioncharacteristics, a yet further aspect of the present invention comprisesa method for the fast retransmission of one or more contiguous TCPsegments. The method comprises the steps of determining that the one ormore contiguous TCP segments previously transmitted on the original TCPconnection to the TCP receiving system need to be retransmitted, the oneor more contiguous TCP segments located between first and second SACKregions of TCP segments and establishing a selective context duplicatedconnection with the TCP receiving system, the selective contextduplicated connection having similar socket and transmissioncharacteristics as the original TCP connection. The method furtherretransmits the one or more contiguous TCP segments to the TCP receivingsystem using the selective context duplicated connection and maintainsthe original TCP connection for on-going transmission of additional TCPsegments to the TCP receiving system and for receipt of communicationsback from the TCP receiving system responsive to the one or morecontiguous TCP segments retransmitted on the selective contextduplicated connection.

In a feature of this present aspect of the invention the step ofdetermining is responsive to receipt by the processor system of twoselective acknowledgments (SACKs) from the TCP receiving system, the twoSACKs identifying the first and second SACK regions, respectively, andwherein the one or more contiguous TCP segments that need to beretransmitted are between the first and second SACK regions. Further,the one or more contiguous TCP segments have a left edge sequence numbercorresponding to the last sequence number of the first SACK region and aright edge sequence number corresponding to the sequence number justprior to the second SACK region. Also, the one or more contiguous TCPsegments comprises a single TCP segment and the one or more contiguousTCP segments comprises a plurality of TCP segments. Additionally, thereception characteristics of the selective context duplicated connectionare disabled and the reception characteristics of the original TCPconnection are not used to define the selective context duplicatedconnection in addition to the original TCP connection and the selectivecontext duplicated connection are linked together through a TCP microengine.

A further feature of the present inventive aspect comprises the step ofcalculating a new RTO timer for the one or more contiguous TCP segmentsthat are retransmitted by the selective context duplicated connectionand loading the value of the RTO timer to the original TCP connection.Further, the on-going transmission of additional TCP segments to the TCPreceiving system using the original TCP connection occurscontemporaneously with the step of retransmitting the one or morecontiguous TCP segments to the TCP receiving system using the selectivecontext duplicated connection. Also, the processor system includes a TCPstate machine and a TCP micro engine and the step of establishing theselective context duplicated connection with the TCP receiving system isperformed by the TCP micro engine after receipt of a retransmissionassistance request from the TCP state engine.

In yet additional features of the present inventive aspect the selectivecontext duplicated connection is closed by the TCP micro engine as soonas the one or more contiguous TCP segments are retransmitted to the TCPreceiving system by the TCP state machine. Additionally, the selectivecontext duplicated connection is closed as soon as the one or morecontiguous TCP segments are retransmitted to the TCP receiving systemand the socket and transmission characteristics of the selective contextduplicated connection are reset and the selective context duplicatedconnection is made available to the processor system for retransmissionuse with another original connection.

The aspect also features the step of creating a data link list for theselective context duplicated connection with pointers pointing to datathat needs to be retransmitted, wherein the data that needs to beretransmitted is included in the one or more contiguous TCP segmentsthat are retransmitted. The aspect further features the step of afterdetermining that the one or more contiguous TCP segments need to beretransmitted, calculating a congestion window size for the original TCPconnection, wherein the selective context duplicated connection isunaffected by the congestion window size of the original TCP connection.

In a processor system for managing TCP communications, the processorsystem managing an original TCP connection with a TCP receiving system,the original TCP connection having socket, transmission, and receptioncharacteristics, a yet additional aspect of the present inventioncomprises a method for the fast retransmission of first and secondgroups of one or more contiguous TCP segments, comprising the steps ofdetermining that the first and second groups of one or more contiguousTCP segments previously transmitted on the original TCP connection tothe TCP receiving system need to be retransmitted, the first group ofone or more contiguous TCP segments preceding a first SACK region of TCPsegments, the second group of one or more contiguous TCP segmentslocated between the first SACK region and a second SACK region of TCPsegments; establishing a selective context duplicated connection withthe TCP receiving system, the selective context duplicated connectionhaving similar socket and transmission characteristics as the originalTCP connection. The method further retransmits the first and secondgroups of one or more contiguous TCP segments to the TCP receivingsystem using the selective context duplicated connection; andmaintaining the original TCP connection for on-going transmission ofadditional TCP segments to the TCP receiving system and for receipt ofcommunications back from the TCP receiving system responsive to thefirst and second groups of one or more contiguous TCP segmentsretransmitted on the selective context duplicated connection.

A feature of this present aspect of the invention comprises the step ofdetermining that the first group of one or more contiguous TCP segmentspreviously transmitted on the original TCP connection to the TCPreceiving system need to be retransmitted is responsive to receipt bythe processor system of a selective acknowledgment (SACK) from the TCPreceiving system, the SACK identifying the first group of one or morecontiguous TCP segments not yet received by the TCP receiving systemthat lie between a last acknowledged TCP segment and the first SACKregion. Further features include the first group of one or morecontiguous TCP segments comprising a single TCP segment and the firstgroup of one or more contiguous TCP segments comprising a plurality ofTCP segments. Additionally, the first group of one or more contiguousTCP segments are defined between a left edge sequence numbercorresponding to the sequence number of the last acknowledged TCPsegment and a right edge sequence number corresponding to the sequencenumber just prior to the first SACK region.

Further featured is the step of determining that the second group of oneor more contiguous TCP segments previously transmitted on the originalTCP connection to the TCP receiving system need to be retransmitted isresponsive to receipt by the processor system of two selectiveacknowledgments (SACKs) from the TCP receiving system, the two SACKsidentifying the first and second SACK regions, respectively. Also, thesecond group of one or more contiguous TCP segments have a left edgesequence number corresponding to the last sequence number of the firstSACK region and a right edge sequence number corresponding to thesequence number just prior to the second SACK region and the secondgroup of one or more contiguous TCP segments comprises a single TCPsegment, wherein the second group of one or more contiguous TCP segmentscomprises a plurality of TCP segments.

In a processor system for managing TCP communications, the processorsystem managing an original TCP connection with a TCP receiving system,the original TCP connection having socket, transmission, and receptioncharacteristics, a yet another additional aspect of the presentinvention comprises a method for the fast retransmission of first andsecond groups of one or more contiguous TCP segments. The methodcomprises the steps of determining that the first group of one or morecontiguous TCP segments previously transmitted on the original TCPconnection to the TCP receiving system need to be retransmitted, thefirst group preceding a first SACK region of TCP segments andestablishing a first selective context duplicated connection with theTCP receiving system, the first selective context duplicated connectionhaving similar socket and transmission characteristics as the originalTCP connection. The method further retransmits the first group of one ormore contiguous TCP segments to the TCP receiving system using the firstselective context duplicated connection and determines that the secondgroup of one or more contiguous TCP segments previously transmitted onthe original TCP connection to the TCP receiving system need to beretransmitted, the second group located between the first SACK regionand a second SACK region of TCP segments; establishing a secondselective context duplicated connection with the TCP receiving system,the second selective context duplicated connection also having similarsocket and transmission characteristics as the original TCP connection.Next, the method retransmits the second group of one or more contiguousTCP segments to the TCP receiving system using the second selectivecontext duplicated connection and maintains the original TCP connectionfor on-going transmission of additional TCP segments to the TCPreceiving system and for receipt of communications back from the TCPreceiving system responsive to the first and second groups of one ormore contiguous TCP segments retransmitted on the first and secondselective context duplicated connections.

A feature of this present aspect of the invention comprises a step ofdetermining that the first group of one or more contiguous TCP segmentspreviously transmitted on the original TCP connection to the TCPreceiving system need to be retransmitted is responsive to receipt bythe processor system of a selective acknowledgment (SACK) from the TCPreceiving system, the SACK identifying the first group of one or morecontiguous TCP segments not yet received by the TCP receiving systemthat lie between a last acknowledged TCP segment and the first SACKregion. Further features of this inventive aspect include the firstgroup of one or more contiguous TCP segments comprising a single TCPsegment, wherein the first group of one or more contiguous TCP segmentscomprise a plurality of TCP segments. Also, the first group of one ormore contiguous TCP segments are defined between a left edge sequencenumber corresponding to the sequence number of the last acknowledged TCPsegment and a right edge sequence number corresponding to the sequencenumber just prior to the first SACK region.

A yet further feature comprises the step of determining that the secondgroup of one or more contiguous TCP segments previously transmitted onthe original TCP connection to the TCP receiving system need to beretransmitted is responsive to receipt by the processor system of twoselective acknowledgments (SACKs) from the TCP receiving system, the twoSACKs identifying the first and second SACK regions, respectively. Alsofeatured in the aspect is the second group of one or more contiguous TCPsegments have a left edge sequence number corresponding to the lastsequence number of the first SACK region and a right edge sequencenumber corresponding to the sequence number just prior to the secondSACK region.

In yet additional features of the present inventive aspect the secondgroup of one or more contiguous TCP segments comprises a single TCPsegment, wherein the second group of one or more contiguous TCP segmentscomprises a plurality of TCP segments. Also, the receptioncharacteristics of the first and second selective context duplicatedconnections are disabled and the reception characteristics of theoriginal TCP connection are not used to define the first and secondselective context duplicated connections. Further, the first and secondselective context duplicated connections do not receive anycommunications back from the TCP receiving system and the original TCPconnection and the first and second selective context duplicatedconnections are linked together by means of a TCP micro engine. Alsofeatured is the step of determining that the first or second group ofone or more contiguous TCP segments previously transmitted on theoriginal TCP comection to the TCP receiving system need to beretransmitted comprises identifying a time out condition associated withthe original TCP connection.

The on-going transmission of additional TCP segments to the receivingTCP system using the original TCP connection occurs contemporaneouslywith the step of retransmitting the first or second group of one or morecontiguous TCP segments to the TCP receiving system using the first orsecond selective context duplicated connections, respectively, whereinthe processor system includes a TCP state machine and a TCP microengine. Also, the step of establishing the first and second selectivecontext duplicated connections with the TCP receiving system isperformed by the TCP micro engine after receipt of retransmissionassistance requests from the TCP state engine, wherein the firstselective context duplicated connection is closed as soon as the firstgroup of one or more contiguous TCP segments are retransmitted to theTCP receiving system. Further, the socket and transmissioncharacteristics of the first selective context duplicated connection arereset and the first selective context duplicated connection is madeavailable to the processor system for retransmission use with anotheroriginal TCP connection. Additionally, the second selective contextduplicated connection is closed as soon as the second group of one ormore contiguous TCP segments are retransmitted to the TCP receivingsystem and the socket and transmission characteristics of the secondselective context duplicated connection are reset and the secondselective context duplicated connection is made available to theprocessor system for retransmission use with another original TCPconnection.

The present invention also encompasses computer-readable medium havingcomputer-executable instructions for performing methods of the presentinvention, and computer networks, state machines, and other hardware andsoftware systems that implement the methods of the present invention.

The above features as well as additional features and aspects of thepresent invention are disclosed herein and will become apparent from thefollowing description of preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and benefits of the present invention will be apparentfrom a detailed description of preferred embodiments thereof taken inconjunction with the following drawings, wherein similar elements arereferred to with similar reference numbers, and wherein:

FIG. 1A is a system view of a conventional TCP/IP communication systemin which the present invention operates;

FIG. 1B is a system view of another conventional TCP/IP communicationsystem in which the present invention operates;

FIG. 2 illustrates conventional TCP/IP layers in which the presentinvention operates;

FIG. 3 illustrates a conventional TCP/IP system for packaging andunpackaging data in a TCP/IP system of the present invention;

FIG. 4A is a timeline illustrating a conventional TCP transmissionsequence;

FIG. 4B is a timeline illustrating a conventional TCP retransmissionsequence;

FIG. 5 is a simplified block diagram of the primary components on thetransmit side of a high speed TCP processor system of the presentinvention;

FIG. 6 is a simplified block diagram of an SCD connection of the presentinvention;

FIG. 7 is a timeline illustrating a TCP transmission and retransmissionsequence using the present invention;

FIG. 8A is a normal transmission condition diagram using an original TCPconnection of the present invention;

FIG. 8B is another normal transmission condition diagram using anoriginal TCP connection of the present invention;

FIG. 9A is a retransmission condition diagram using an SCD connection ofthe present invention;

FIG. 9B is another retransmission condition diagram using an SCDconnection of the present invention;

FIG. 9C is yet another retransmission condition diagram using an SCDconnection of the present invention;

FIG. 10 illustrates a table of parameters copied from an originalconnection to an SCD connection of the present invention;

FIG. 11 illustrates a table of the connection status bit formats of thepresent invention;

FIG. 12A is a retransmission condition diagram using an SCD connectionof the present invention;

FIG. 12B is another retransmission condition diagram using an SCDconnection of the present invention;

FIG. 13A is a slow start retransmission condition diagram using an SCDconnection of the present invention;

FIG. 13B is a continuing slow start retransmission condition diagramusing an SCD connection of the present invention;

FIG. 14 is a flowchart for a TCP window calculator of the presentinvention;

FIG. 15 is a schematic of an exemplary TCP transmit effective windowcalculator of the present invention;

FIG. 16 is a schematic of an exemplary TCP transmit application remainwindow calculator of the present invention;

FIG. 17 is a table of the input parameter protocols for TCP windowcalculator of FIG. 14;

FIG. 18 is a table of the outputs for two clock cycles for the TCPwindow calculator of FIG. 14;

FIG. 19 is a table of the outputs for three clock cycles for the TCPwindow calculator of FIG. 14;

FIG. 20 is a table of the outputs for five clock cycles for the TCPwindow calculator of FIG. 14;

FIG. 21 is a clock sequence diagram illustrating the timing of the TCPwindow calculator of FIG. 14.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In conventional TCP software systems accessed by a CPU or in aconventional TOE device, it is relatively easy to manage thetransmission, retransmission, and fast retransmission of lost, delayed,or mis-communicated segments. For example, it generally costs severalhundred clock cycles to retransmit TCP segments along an original TCPconnection. In other words, a conventional TCP system is only capable ofrunning at a processing speed of approximately 1 gigabit (Gbit) persegment when required to retransmit lost, delayed, or previouslymis-communicated TCP segments. There is also no significant degradationof performance, at this slow processing speed, when using the same ororiginal TCP connection to handle original transmissions and anynecessary retransmissions.

Some aspects of transmitting and retransmitting segments in aconventional TCP system are illustrated, for comparison purposes, inFIGS. 4A and 4B. Turning first to FIG. 4A, timeline 400 a illustrates anormal TCP transmission in which the source machine sends segments 0through 5 (Seg 0 . . . . Seg 5) in sequence, as designated by blocks402,403,404,405,406, and 407. Upon the sending of each respectivesegment, variables (snd_max and send_nxt) maintained by the sourcemachine are updated. For example, when segment 0 is sent, the snd_maxvariable 412 (designated as snd_max0 since segment 0 has already beensent) is updated to have a value equal to the first sequence number ofthe next segment (i.e., segment 1) that needs to be transmitted. Thesend_nxt variable 422 (also designated as send_nxt0 since segment 0 hasbeen sent) is updated to the same value since segment 1 is the segmentthat needs to be sent next. This process proceeds for each successfulsegment transmitted. As long as the transmitted segments are receivedproperly and acknowledged (ACKed) by the TCP receiver system(destination machine), the snd_max and send_nxt of the source machinefor this transmission remain in sync and at the same value. However,suppose that after sending segment 5, designated by block 407, thesource machine receives three identical ACKs of the first sequencenumber of segment 2, which corresponds to the snd_una variable ofsegment 1 (maintained by the destination machine for this transmission).When this occurs, the source machine causes this particular TCPconnection to go into a “fast retransmit” mode, in conventional manner.As shown on the timeline 400 b of FIG. 4B, “fast retransmit” mode causesthe send_nxt variable 442 for this TCP connection to point back(temporarily) to the value it had at send_nxtl. The snd_max valueremains at snd_max5 447. This means that the “normal” TCP transmissionis temporarily stopped because the send_nxt pointer has to move. Segment2, designated by block 444, is then retransmitted along the same TCPconnection. Then the source machine resets the send_nxt variable forthis TCP connection back to the value it had when it entered “fastretransmit” mode, which in this example is send_nxt5. This TCPconnection then resumes sending the next in-order segment (i.e., segment6) in conventional manner.

In-order to handle connections on the order of 1000 s and 10,000 s usinga single TOE device and in order to achieve processing speeds exceeding10 GHz, however, it is preferable to streamline the bulk of the TCPprocessing to a TOE device comprising a TCP state machine having accessto a limited amount of memory capacity on the same integrated circuit.When this is done, it is not feasible to use both the send_nxt andsnd_max variables for every connection handled by the TOE device. Thereason for this is because each send_nxt parameter takes up 4 bytes ofmemory per connection. Thus, if the TOE device is expected to manage1000+ connections simultaneously, this uses up 4 kbytes of limitedmemory just to store this one parameter, which, as was explained withreference to FIGS. 4A and 4B, is in most circumstances redundant withthe snd_max variable.

For systems, such as the present invention, which are designed toaccommodate a large number of high-speed connections in a limited memoryenvironment, successful management of the large number of high speed TCPconnections becomes problematic. The present invention solves thisproblem in two ways. First, instead of allowing all available TCPconnections to be used for retransmission purposes, only a specified,limited number of the total available connections of the TOE device arededicated to retransmission tasks. Such retransmission connections,which will be called selective context duplication (SCD) or “clone”connections hereinafter, are made available to work in conjunction withany one of the original or primary TCP connections for retransmissionpurposes on a rolling basis. This is a viable solution because intypical TCP communications, less than 10% of all TCP communications areneeded for retransmission traffic. Thus, in the present invention,between 16 and 32 per each 1024 connections may be allocated forretransmission tasks only. Second, the present invention does not usethe send_nxt variable. Instead, the present invention introduces a newvariable or parameter, appl_init_seq, which is usable not only by theoriginal or primary TCP connections but also by the SCD or cloneconnections. This new variable not only allows each TCP connection tobuild segments for normal transmission more quickly, but also providesthe necessary parameter for building retransmission segments, while onlyusing 1.22 kbytes of memory capacity. Details of SCD connections and theappl_init_seq parameter will be discussed in greater detail hereinafter.

Turning first to FIG. 5, a simplified block diagram showing the primarycomponents on the transmit side of a high-speed TCP processor system 500of the present invention are illustrated. The TCP processor system 500includes a TCP state engine that interacts and interfaces with softwareapplications 550 of the source machine and with at least one TOE microengine 580. The TCP processor system 500 includes applicationsegmentation processors 502, a packet FIFO buffer 504, a transmit packetpayload builder 506, a memory control interface 508, external memory510, a local transmit buffer 512, a TCP header insertion buildingcomponent 514, a TCP transmit processor 520, connection context memory522, a transmission physical layer FIFO interface 516, and a physicallayer or PHY component 518.

When an application 550 needs to send data to a destination machine,application transmission requests 545 are sent to a respectiveapplication segmentation processor 502, which determines how therelevant data will be divided into appropriate segment size chunks ofinformation. This determination information and relevant pointers areloaded into packet transmit FIFO 504, which forwards the same to thetransmit packet payload builder 506. The transmit packet payload builder506 cooperates with the memory control interface 508 to extract theactual application data from memory 510, which is forwarded to the localtransmission buffer 512, which contains TCP segment payload and datasegment information. The TCP header insertion building component 514takes this information from the local transmission buffer 512 and“checks it in” with the TOE transmit processor 520. TCP header insertionbuilding component 514 passes the appl_init_seq parameter, payload size,and connection number to the TOE transmit processor 520. The TOEtransmit processor 520 extracts other necessary variables and parametersfrom the connection context memory 522 and then “checks out” the segmentback to the TCP header insertion building component 514. The TCP headerinsertion building component 514 then forwards the segment to thetransmission PHY interface 516, where it is forward on to the remaininglayers of the TCP/IP stack for addition of IP and Ethernet headers andtails prior to transmission in conventional manner.

Turning now to FIG. 6, a simplified block diagram 600 illustrates theprocess of creating and using an SCD connection to advantage. In asource machine 610 managing a large plurality of TCP connections,software applications 620 interface with the TCP processor system of thepresent invention. The TCP processor system includes a TCP state machine630 and one or more TCP micro engines 640. Each primary TCP connectionhas an original, dedicated connection 632. The connection parameters orcharacteristics (socket, addressing, reception, etc.) for each originalTCP connection is managed by the one or more TCP micro engines 640. Datafor each original TCP connection hits a transmit buffer 650 that assistsin the ordering and packaging of each data packet at the IP and Ethernetlayers of the TCP/IP stack prior to actual transmission. Whenever aretransmission situation occurs with any original TCP connection, theTCP micro engine 640 is responsible for creating an SCD connection 634associated with the original TCP connection that is in retransmit mode.As stated previously, if a particular TCP state machine 630 is handlingon the order of 1000 simultaneous TCP connections, between 16 and 32 SCDconnections are available on a rolling basis to the TCP processor systemfor use in association with any of the original TCP connections 632 thatneed retransmission assistance.

It should be understood that each SCD connection 634 is set up andestablished as a transmission-side-only TCP connection. Preferably, itcontains only a transmission side configuration without the receive sideconfiguration or with the receive side configuration disabled. It hasall the same parameters from IP layer three down. However, the TCP layerfor the SCD connection 634 does not contain any TCP timers or any roundtrip timing capability.

When the TCP state engine 630 detects a fast retransmit condition for aparticular original TCP connection (i.e., by receiving three or moreconsecutive duplicate ACKs from the TCP receiver system), the TCP stateengine 630 generates a message or request to the TCP micro engine 640for retransmission assistance.

The TCP micro engine 640 then builds an SCD connection associated orlinked with the original TCP connection that asked for retransmissionassistance. The SCD connection 634 has similar socket and transmissioncharacteristics as the original TCP connection 632 with which it isassociated with a few minor differences. The SCD connection 634 and itsassociated original TCP connection 632 are worked side by side as asingle “connection set.” This is accomplished by the TCP micro engine640, which links the original TCP connection 632 and SCD connection 634together through messages. The SCD connection 634 is used forretransmission only—its receive side is disable. On the other hand, theoriginal TCP connection 632 is used for both transmission and receptionprocessing.

The TCP micro engine 640 performs the following tasks for fastretransmission: (i) it sets up the SCD connection 634 by copying most ofthe parameters or characteristics from the original TCP connection 632.But the receive side of the SCD connection 634 is disable so that allacknowledgments (ACKs) back from the TCP receiver system of thedestination machine are received by the original TCP connection 632 asnormal. Hardware within the TCP state machine 630 also uses a one bitvariable to indicate that this particular TCP connection is being usedonly as an SCD connection; (ii) it copies the snd_una variable of theoriginal TCP connection 632 to the snd_una, sent_max and appl_init_seqvariable of the associated SCD connection 634; (iii) it writes onemaximum segment size (MSS) value or the total unacknowledged (unACKed)flightsize data between snd_una and sent_max (whichever is smaller) fromthe original TCP connection 632 to the rmt_offer_win variable of the SCDconnection 634; (iv) it creates a data link list for the SCD connection634 by setting pointers pointing to required retransmission data; (v) itcalculates new RTO timer values and loads the value back to the RTOtimer of the original TCP connection 632; (vi) it enables hardwaremessage generation as the SCD connection 634 completes retransmittingone or more segments; (vii) it enables hardware for SCD connectiontransmission. The TCP state machine 630 sends a message to the TCP microengine 640 when the SCD connection completes retransmission. Once theretransmission is complete, the TCP micro engine 640 “tears down” orreleases the SCD connection 634 for further retransmission usage withthe same or with any of the other original TCP connections 532 that needretransmission assistance.

Timeline 700 of FIG. 7, in contrast with the timelines of FIGS. 4A and4B, illustrates how the present invention handles transmission andretransmission of TCP segments. Similar to FIG. 4A, timeline 700illustrates transmission of segments 0 through 5 (Seg 0 . . . . Seg 5)in sequence, as designated by blocks 702,703,704,705,706, and 707. Toaccomplish the transmission/retransmission of the present invention, anew internal variable, appl_init_seq #, is introduced and is used inplace of the send_nxt variable. Different from the send_nxt variable,this appl_init_seq variable is used to identify the initial sequencenumber of the next TCP segment to be built for transmission. As shown inFIG. 7, the value of this variable is always later than or equal to thesnd_max variable. Because of this feature, the present invention enablesthe application segmentation interface to build TCP segments prior toactual transmission and to store those TCP segments in a temporarytransmission buffer as long as the total amount of data does not exceedthe size of remote offer window limit.

This appl_init_seq sequence number is checked into the TCP stack fortransmission tracking. The value of the appl_init_seq variable for eachsegment plus the data size is the new snd_max value. If the segment iswithout payload, then the appl_init_seq is preferably ignored by thesystem. The sequence number of the zero payload segment is extractedfrom the previously-stored snd_max value from memory. By doing this, theSCD connection can be built solely for the purpose of retransmitting TCPsegments that need to be retransmitted.

More specifically, upon the sending of each respective TCP segment, thesnd_max variable is updated. Thus, when segment 0 is sent, the snd_maxvariable 712 (designated as snd_max0 since segment 0 has already beensent) is updated to have a value equal to the first sequence number ofthe next segment (i.e., segment 1) that needs to be transmitted. Whenthe TCP processor system builds and checks in segment 1, which carries astart sequence number equal to the value of variable appl_init_seq 1,for transmission, the snd_max variable is assigned a value equal toappl_init_seq 1 plus the payload size of segment 1. This processproceeds for each successful TCP segment built and transmitted.

When a TCP segment needs to be retransmitted, the snd_max variable forthe original TCP connection is not changed. The snd_una value that hasbeen ACKed back three or more times from the TCP receiver system,indicating that the next segment following that snd_una sequence numberhas not yet been received and needs to be retransmitted, is then used todefine the appl_init_seq value for the SCD connection.

As has been and will be discussed in greater detail herein, an SCDconnection is used by the TCP processor system of the present inventionto retransmit in fast retransmit mode a single TCP segment, in responseto three or more duplicate ACKs, when SACK tracking is not enabled. AnSCD connection is also usable to retransmit in fast retransmit mode aplurality of TCP segments between a last ACKed segment and a first SACKregion or between two SACK regions. A single SCD connection can be usedto retransmit two groups of one or more TCP segments associated with aparticular original TCP connection or two separate SCD connections maybe used, one for each group of one or more TCP segments associated witha particular original TCP connection. An SCD connection is also used bythe present invention to retransmit TCP segments for an associatedoriginal TCP connection after a retransmission time out condition on theoriginal TCP connection.

Turning now to FIG. 8A, a normal transmission condition diagram 800 ausing an original TCP connection of the present invention isillustrated. FIG. 8A illustrates the situation when a TCP connection hasbeen established, with all TCP parameters initialized, and when TCPsegments are being transmitted by the TCP processor system of the sourcemachine and received by the TCP receiver system at the destinationmachine. For this example, it is assumed that SACK tracking is off, isnot being used, or no SACK regions have been acknowledged. The diagram800 a includes a transmission sequence number timeline 802. As shown onthe timeline 802, segment 1 through segment 6 comprise the flightsize810 of TCP segments that have already been transmitted by the TCPprocessor system using the original TCP connection. Segment 7 throughsegment 14 represent those TCP segments that have been built by the TCPprocessor system but not yet transmitted on the line. The snd_unavariable 812 represents the last sequence number ACKed by the TCPreceiver system. The snd_max variable 814 represents the last sequencenumber of the last TCP segment that has already been sent and that hasbeen “checked into” the TCP processor system. The appl_init_seq variable816 represents the start sequence number of the next TCP segment to bebuilt by the processor system. It should be noted here that when the TCPprocessor system is reset, the appl_init_seq variable 816 and thesent_max variable 814 start out as the same value but as TCP segmentsare built and transmitted, the appl_init_seq variable 816 gets out aheadof the sent_max variable 814, as shown in FIG. 8.

The send window for this original TCP connection uses the snd_unaacknowledged value 812 as a base reference point. In this example, thecongestion window 842, which is defined between the snd_una value 812and congestion window (cwnd) right edge 818, is less than the remoteoffer window 844, which is defined between the snd_una value 812 and theremote offer window right edge 820. The TCP effective window 852 isdefined between the sent_max value 814 and whichever is the closer of(i) the congestion window (cwnd) right edge 818 and (ii) the remoteoffer window right edge 820, which, in this example, is the congestionwindow (cwnd) right edge 818. The application transmit remain window 854is defined as a positive value and includes whatever portion of the TCPeffective window 852 that exceeds or is beyond the appl_init_seqvariable 816.

Turning now to FIG. 8B, a normal transmission condition diagram 800 busing an original TCP connection of the present invention when thecongestion window 842 is greater than the remote offer window 844 isillustrated. In this example, the congestion window 842, which isdefined between the snd_una value 812 and congestion window (cwnd) rightedge 818, is greater than the remote offer window 844, which is definedbetween the snd_una value 812 and the remote offer window right edge820. Again, the TCP effective window 852 is defined between the sent_maxvalue 814 and whichever is the closer of (i) the congestion window(cwnd) right edge 818 and (ii) the remote offer window right edge 820,which, in this particular example, is the remote offer window right edge820. The application transmit remain window 854 is defined as a positivevalue and includes whatever portion of the TCP effective window 852 thatexceeds or is beyond the appl_init_seq variable 816.

FIG. 9A now illustrates a retransmission condition diagram 900 a whenthe present invention uses an SCD connection 931 for retransmissionassistance, fast recovery condition at a third duplicate ACK received byan original connection 901. FIG. 9A illustrates the situation when anoriginal TCP connection 901 has been established, with all TCPparameters initialized, and when TCP segments are being transmitted bythe TCP processor system of the source machine and received by the TCPreceiver system at the destination machine. Again, in this example, SACKtracking is off, is not being used, or no SACK regions have beenacknowledged. The diagram 900 a includes an original transmissionsequence number timeline 902. As shown on the timeline 902, segment 1through segment 12 comprise the flightsize 910 of TCP segments that havealready been transmitted by the TCP processor system using the originalTCP connection 901. Segment 13 through segment 14 represent those TCPsegments that have been built by the TCP processor system but not yettransmitted on the line. The snd_una variable 912 represents the lastsequence number ACKed by the TCP receiver system. The snd_max variable914 represents the last sequence number of the last TCP segment that hasalready been sent and that has been “checked into” the TCP processorsystem. The appl_init_seq variable 916 represents the start sequencenumber of the next TCP segment to be built by the processor system.

In this example, when the same snd_una variable 912 has been receivedthree times (i.e., a third duplicate ACK) the TOE receive processorsends a fast retransmission request message to the microengine torequest creation of an SCD connection 931 for retransmission of the lostTCP segment 962 that has a sequence number immediately following thevalue of the send-una variable 912. The TOE receive processor also setsa fast_rexmit_mtx variable (not shown) associated with the originalconnection 901 to a “high” value to indicate that the originalconnection is in a fast retransmission mode. This fast_rexmit_mtxvariable is reset as soon as acknowledgment of retransmitted data isreceived back by the original connection.

The congestion window 942 is defined between the snd_una value 912 andthe congestion window (cwnd) right edge 918 a. The congestion window(cwnd) right edge 918 a is equal to half the flightsize plus 3 maximumsegment size (MSS). In this example, because the flightsize is twelvesegments, the congestion window (cwnd) right edge 918 a is set to theright edge of segment 9. The TCP effective window 952 a is definedbetween the sent_max value 914 and the congestion window (cwnd) rightedge 918 a, which in this example defines a negative value. Since anegative value is meaningless, the system sets the TCP effective window952 a to zero. Likewise, the application transmit remain window 954 a isdefined to include whatever portion of the TCP effective window 952 athat exceeds or is beyond the appl_init_seq variable 916. Since anegative value is meaningless, the system also sets the applicationtransmit remain window 954 a to zero.

For the SCD connection 931, as shown on the timeline 932, the snd_unavariable 922 is set to the same value as the snd_una variable 912 of theoriginal connection 901. The remote offer window right edge 920 is setto the right edge value of the lost segment 962; thus, the remote offerwindow 944 for the SCD connection 931 is only one MSS, defined betweenthe snd_una value 922 and the remote offer window right edge 920. Thesnd_max variable 924 and appl_init_seq variable 926 for the SCDconnection 931 are set to the same value as the snd_una variable 922.The TCP effective window 952 b for the SCD connection 931 is set to thesize of the lost segment 962, which in this case is 1 MSS. Likewise, theapplication transmit remain window 954 b for the SCD connection 931 isset to the size of the lost segment 962, which in this case is 1 MSS.Firnware requires that the RTO timer of the original connection 901 bereloaded after retransmission of the lost segment 962.

FIG. 9B illustrates a retransmission condition diagram 900 b after thepresent invention has used an SCD connection 931 for retransmissionassistance of a single lost segment 962 and after more than threeduplicate ACKs have been received by the original connection 901. Asshown, segments 13 and 14 have now been transmitted along the originalconnection 901 contemporaneously with SCD connection 931 being used toretransmit lost segment 962. Thus, the snd_max variable 914 has “caughtup to” the appl_init_seq variable 916 and flightsize 910 now is equal tofourteen segments.

The congestion window 942 is still defined between the snd_una value 912and the congestion window (cwnd) right edge 918. Once lost segment 962has been retransmitted, the congestion window (cwnd) right edge 918advances one MSS (from the value it was set to in FIG. 9A) because oneTCP segment size has been retransmitted by the SCD connection 931. Thus,the congestion window (cwnd) right edge 918 is set to the right edge ofsegment 10. The TCP effective window 952 a is still negative so thesystem sets it to zero. Likewise, the application transmit remain window954 a is negative so the system sets it to zero as well.

Turning now to the SCD connection 931, once the lost segment 962 isretransmitted, the snd_max variable 924 and appl_init_seq variable 926for the SCD connection 931 advance to the last sequence number of thelost segment 962. The congestion window right edge 918 for the SCDconnection 931 does not advance. Once the lost segment 962 isretransmitted by the SCD connection 931, hardware sends a message to themicro engine to tear down the SCD connection 931 for this particularoriginal connection 901 to make it available to another originalconnection that needs retransmission assistance.

FIG. 9C illustrates a retransmission condition diagram 900 c and theimpact on the variables and segments of the original connection 901after lost segment 962 has been retransmitted on an SCD connection andafter the original SCD connection 901 has received numerous duplicateACKs for the lost segment 962. It will be recalled that, for eachduplicate ACK received, the congestion window (cwnd) right edge 918 aadvances one MSS. FIG. 9C illustrates the impact of the advance of thecongestion window (cwnd) right edge 918 a past the snd_max variable 914and the appl_init_seq variable 916. When the congestion window 942 openspast the snd_max variable 914 and the appl_init_seq variable 916, theTCP effective window 952 a becomes positive, the application transmitremain window 954 a becomes positive, and the original connection 901resumes creation of new TCP segments for transmission and resume actualtransmission up to the congestion window right edge 918 a value.

FIG. 10 illustrates a table 1000 of parameters 1010 that are copied froman original connection to an associated SCD connection for use inretransmission. The table 1000 includes columns for the bit size 1020and a brief description 1030 of each corresponding parameter 1010.

FIG. 11 illustrates a table 1100 of the connection status (cnn_stat) bitformat for the 32 address bits for this parameter. Column 1110 shows thebit range, column 1120 includes a brief description for the use of thebits for the corresponding bit range, and column 1130 includes a moredetailed description for the use of the bits for the corresponding bitrange.

Turning now to FIG. 12A, a retransmission condition diagram 1200 aillustrates use of an SCD connection 1231 for retransmission assistance,fast recovery condition at a third duplicate SACK received by anoriginal connection 1201. FIG. 12A illustrates the situation when anoriginal TCP connection 1201 has been established, with all TCPparameters initialized, and when TCP segments are being transmitted bythe TCP processor system of the source machine and received by the TCPreceiver system at the destination machine. In this example, SACKtracking is on. The diagram 1200 a includes an original transmissionsequence number timeline 1202. As shown on the timeline 1202, segment 1through segment 12 comprise the flightsize 1210 of TCP segments thathave already been transmitted by the TCP processor system using theoriginal TCP connection 1201. Segment 13 through segment 14 representthose TCP segments that have been built by the TCP processor system butnot yet transmitted on the line. The snd_una variable 1212 representsthe last sequence number ACKed by the TCP receiver system. The snd_maxvariable 1214 represents the last sequence number of the last TCPsegment that has already been sent and that has been “checked into” theTCP processor system. The appl_init_seq variable 1216 represents thestart sequence number of the next TCP segment to be built by theprocessor system.

In this example, SACK range1 1273 indicates that segment 4 throughsegment 8 have been received. SACK range2 1275 indicates that segment 11and segment 12 have also been received. Thus, based on the snd_una 1212and the SACK range1 1273 values, the system can determine that threesegments 1263 (segment 1 through segment 3) have been lost. Based on theSACK range1 1273 and SACK range2 1275, the system can determine that twosegments 1265 (segment 9 through segment 10) have been lost. When theoriginal connection 1202 receives the same snd_una variable 1212 threeconsecutive times (i.e., a third duplicate ACK) the TOE receiveprocessor sends a fast retransmission request message to the microengineto request creation of an SCD connection 1231 for retransmission of thefirst set of lost TCP segments 1263 that have a sequence rangeimmediately following the value of the send-una variable 1212 and endingwith the left edge of SACK range1 1273. The TOE receive processor sets afast_rexmit_mtx variable (not shown) associated with the originalconnection 1201 to a “high” value to indicate that the originalconnection is in a fast retransmission mode. This fast_rexmit_mtxvariable is reset as soon as acknowledgment of retransmitted data isreceived back by the original connection 1201.

The congestion window 1242 is defined between the snd_una value 1212 andthe congestion window (cwnd) right edge 1218 a. The congestion window(cwnd) right edge 1218 a is initially equal to half the flightsize plus3 maximum segment size (MSS). In this example, because the flightsize istwelve segments, the congestion window (cwnd) right edge 1218 a is setto the right edge of segment 9. The TCP effective window 1252 a isdefined between the sent_max value 1214 and the congestion window (cwnd)right edge 1218 a, which in this example defines a negative value. Sincea negative value is meaningless, the system sets the TCP effectivewindow 1252 a to zero. Likewise, the application transmit remain window1254 a is defined to include whatever portion of the TCP effectivewindow 1252 a exceeds or is beyond the appl_init_seq variable 1216.Since a negative value is meaningless, the system also sets theapplication transmit remain window 1254 a to zero.

For the SCD connection 1231, as shown on the timeline 1232, the snd_unavariable 1222 is set to the same value as the snd_una variable 1212 ofthe original connection 1201. The remote offer window right edge 1220 bis set to the right edge value of the first group of lost segments 1263;thus, the remote offer window 1244 b for the SCD connection 1231 isthree MSS, defined between the snd_una value 1222 and the remote offerwindow right edge 1220 b. The snd_max variable 1224 and appl_init_seqvariable 1226 for the SCD connection 1231 are set to the same value asthe snd_una variable 1222. The TCP effective window 1252 b for the SCDconnection 1231 is set to the size of the first group of lost segments1263, which in this case is three MSS. Likewise, the applicationtransmit remain window 1254 b for the SCD connection 1231 is set to thesize of the first group of lost segments 1263, which in this case isthree MSS. Firmware requires that the RTO timer of the originalconnection 1201 be reloaded after retransmission of the first group oflost segments 1263.

Turning now to FIG. 12B, a retransmission condition diagram 1200 billustrates use of an SCD connection 1231 for retransmission assistance,fast recovery condition at a third duplicate SACK received by anoriginal connection 1201 for retransmission of the second group of lostsegments 1265.

For the SCD connection 1231, as shown on the timeline 1232, the snd_unavariable 1282 is set to the same value as the snd_una variable 1212 ofthe original connection 1201. The remote offer window right edge 1220 cis set to the right edge value of the second group of lost segments1265; thus, the remote offer window 1244 c for the SCD connection 1231for retransmission of the second group of lost segments 1265 is two MSS,defined between the snd_una value 1282 and the remote offer window rightedge 1220 c. The snd_max variable 1284 and appl_init_seq variable 1286for the SCD connection 1231 are set to the same value as the sequencenumber of the right edge of the SACK region1 1273. The TCP effectivewindow 1252 c for the SCD connection 1231 for retransmission of thesecond group of lost segments 1265 is set to the size of the secondgroup of lost segments 1265, which in this case is two MSS. Likewise,the application transmit remain window 1254 c for the SCD connection1231 for retransmission of the second group of lost segments 1265 is setto the size of the second group of lost segments 1265, which in thiscase is two MSS. Firmware requires that the RTO timer of the originalconnection 1201 be reloaded after retransmission of the second group oflost segments 1265. The micro-engine ensures that the congestion window1218 c remains sufficiently beyond the right edge of the second group oflost segments 1265 to handle the retransmission of the second group oflost segments 1265.

Turning now to FIG. 13A, a retransmission condition diagram 1300 a whenthe present invention uses an SCD connection 1331 for slow startretransmission assistance when there has been a retransmission timeout(RTO) condition on the original connection 1301. FIG. 13A illustratesthe situation when an original TCP connection 1301 has been established,with all TCP parameters initialized, and when TCP segments have beentransmitted by the TCP processor system of the source machine andreceived by the TCP receiver system at the destination machine. In thisexample, SACK tracking may be on or off—it is irrelevant here sincethere has been a timeout condition since the last acknowledged TCPsegment. The diagram 1300 a includes an original transmission sequencenumber timeline 1302. As shown on the timeline 1302, segment 1 throughsegment 15 comprise the flightsize 1310 of TCP segments that havealready been built and transmitted by the TCP processor system using theoriginal TCP connection 1301. In this example, there are no TCP segmentsthat have been built by the TCP processor system but not yet transmittedon the line; thus, the snd_max variable 1314, which represents the lastsequence number of the last TCP segment that has already been sent andthat has been “checked into” the TCP processor system, and theappl_init_seq variable 1316, which represents the start sequence numberof the next TCP segment to be built by the processor system, are at thesame value. The snd_una variable 1312 still represents the last sequencenumber ACKed by the TCP receiver system before it went into time outcondition.

In this example, when the RTO timer of the original connection 1301times out (i.e., does not receive any ACKs or SACKs in a predeterminedperiod of time), the TOE receive processor sends an RTO retransmissionrequest message to the microengine to request creation of an SCDconnection 1331 for retransmission of the TCP segments from theflightsize 1310 starting with the TCP segment that has a sequence numberimmediately following the value of the send-una variable 1312. The TOEreceive processor also sets a fast_rexmit_mtx variable (not shown)associated with the original connection 1301 to a “high” value toindicate that the original connection is in SCD retransmission mode.This fast_rexmit_mtx variable is reset as soon as acknowledgment ofretransmitted data is received back by the original connection 1301.

Just prior to the time out condition, the congestion window of theoriginal connection 1301 was defined between the snd_una value 1312 andthe “old” congestion window (cwnd) right edge 1318 a. At time out, thecongestion window 1342 b is set to one MSS or 2 MSS, by conventional TCPprotocol. In this example, it is set to one MSS wherein the congestionwindow 1342 b is defined between the snd_una value 1312 and the RTOcongestion window right edge 1318 b. At time out, the TCP effectivewindow 1352 a and the application transmit remain window 1354 a bothbecome negative and, therefore, are set to zero by the system. Theremote offer window 1344 a of the original connection 1301 is andremains defined between the snd_una value 1312 and the remote offerwindow right edge 1320 a.

For the SCD connection 1331, as shown on the timeline 1332, the snd_unavariable 1322 is set to the same value as the snd_una variable 1312 ofthe original connection 1301. The remote offer window right edge 1320 bis set to the right edge value of the RTO congestion window 1342 b;thus, the remote offer window 1344 b for the SCD connection 1331 is onlyone MSS, defined between the snd_una value 1322 and the remote offerwindow right edge 1320 b. The snd_max variable 1324 and appl_init_seqvariable 1326 for the SCD connection 1331 are initially set to the samevalue as the snd_una variable 1322. The TCP effective window 1352 b forthe SCD connection 1331 is initially set to the size of the TCPsegment(s) 1364 to be retransmitted first in RTO condition, which inthis case is one MSS. Likewise, the application transmit remain window1354 b for the SCD connection 1331 is initially set to the size of theTCP segment(s) 1364 to be retransmitted first in RTO condition, which inthis case is one MSS.

Firmware causes the TCP stack to prepare the first TCP segment 1364 forretransmission and prepares the RTO load value for the originalconnection 1301 as if an ACK has been returned. The hardware TCP receiveprocessor loads the RTO time value. Firmware also keeps the snd_unavalue 1312 of the original connection to prepare the total amount ofdata for the next retransmission iteration. As soon as the segment 1364has been retransmitted, hardware sends a message to the microengine tobreak down this SCD connection 1331 so that it can be used forretransmission purposes with this same original connection 1301 or withanother original connection (not shown).

FIG. 13B illustrates a retransmission condition diagram 1300 b showingthe continuing retransmission process after segment 1364 has beenretransmitted and acknowledged as received after a time out condition onthe original connection 1301. When the original connection is in RTOcondition, no further TCP segments are built or transmitted by theoriginal connection 1301 until the snd_una value 1312 catches up to thesent_max value 1314. Thus, there is no further change to theappl_init_seq value 1316, the flightsize 1310, the TCP effective window1352 a of the original connection 1301, and the application transmitremain window 1354 a of the original connection 1301. When anacknowledgment is received by the original connection 1301 for segment1364, the snd_una value 1312 advances. The size of the congestion window1342 b expands by one MSS, as shown by the advance of the congestionwindow right edge 1318 b. Hardware sends a retransmission requestmessage to the microengine, which builds an SCD connection 1331 for RTOretransmission assistance for additional TCP segments 1365.

For the SCD connection 1331, as shown on the timeline 1332, the snd_unavariable 1322 is again set to the same value as the updated snd_unavariable 1312 of the original connection 1301. The remote offer windowright edge 1320 b is set to the right edge value of the RTO congestionwindow 1342 b; thus, the remote offer window 1344 b for this SCDconnection 1331 is now two MSS, defined between the snd_una value 1322and the remote offer window right edge 1320 b. The snd_max variable 1324and appl_init_seq variable 1326 for this SCD connection 1331 are againinitially set to the same value as the snd_una variable 1322. The TCPeffective window 1352 b for this SCD connection 1331 is set to the sizeof the TCP segment(s) 1365 to be retransmitted in RTO condition, whichin this case is two MSS. Likewise, the application transmit remainwindow 1354 b for this SCD connection 1331 is set to the same size,which in this case is two MSS.

Firmware causes the TCP stack to prepare the second TCP segments 1365for retransmission and prepares the RTO load value for the originalconnection 1301 as if an ACK has been returned. The hardware TCP receiveprocessor loads the RTO time value. Firmware also keeps the snd_unavalue 1312 of the original connection to prepare the total amount ofdata for the next retransmission iteration. As soon as the segments 1365have been retransmitted, hardware sends a message to the microengine tobreak down this SCD connection 1331 so that it can be used forretransmission purposes with this same original connection 1301 or withanother original connection (not shown). This process will repeat untilall TCP segments from the flightsize 1310 have been retransmitted. Thesize of the congestion window 1342 b for the SCD connection 1331 issized and can be expanded based on conventional TCP protocol for slowstart retransmission in an RTO condition.

Improved Low-memory TOE Window Calculator

The processing of TCP/IP data traffic utilizes a significant amount of aserver's processing resources. Due to the reality that datacommunication speeds have increased faster than processor speeds, aresulting problem is that processors, which are primarily designed forprocessing functions and not I/O functions, have developed significanttrouble keeping up with and maintaining data flow through currentnetwork systems. A significant result of this problem is that TCP/IPdata flow is processed at a slower rate than the speed of the networkupon which the data is transmitted.

The fore-mentioned problem has been remedied by the use of TCP OffloadEngine (TOE) technology. Within a communications network, a TOE assumesthe function of translating all or specific parts of a TCP/IPtransmission. Conventional TOE technology takes advantage of knownsoftware extensions to existing TCP/IP stacks, wherein these extensionsallow for the use of hardware data planes that can be realized on TOENetwork Interface Cards (TNICs).

The primary purpose for TCP is to provide a reliable host-to-hostprotocol between hosts in packet-switched computer communicationnetworks. TCP has the further capability to recover information fromdata that is damaged, lost, duplicated, or delivered out of order. Theability to recover data is achieved by TCP assigning a sequence numberto each transmitted data packet, and requiring a positive acknowledgment(ACK) from the receiving system. If the ACK is not received within adetermined timeout interval the data packet is retransmitted. At thereceiver, the sequence numbers are used to correctly order segments thatmay be received out of order and to eliminate duplicates. Damage ishandled by adding a checksum to each segment transmitted, checking it atthe receiver, and discarding damaged segments.

TCP further provides a means for a receiving system to govern the amountof data that is transmitted by a sender. This aspect is accomplished byreturning a “window” with every ACK, wherein the window indicates anacceptable range of sequence numbers beyond the last segmentsuccessfully received. The window indicates an allowed number of datapackets that the sender may transmit before receiving further permissionto transmit additional data. A window's primary function is that ofcontrolling the congestion of transmitted data. A network connectionwill have a bottleneck somewhere wherein the transmitted data can onlybe handled so fast. If the transmission of data occurs too fast, thebottleneck will be surpassed; thus, resulting in lost data unless thebottleneck is equal to the transmitting speed of the transmitting host.A TCP window throttles the transmission speed to a level wherecongestion and data loss do not occur.

In order to properly maintain a TCP connection, several variables areconventionally utilized to accomplish the foreseen features of a TCPtransmission. The TCP transmission variables are stored in atransmission connection record called a Transmission Control Block(TCB). Among the variables stored in the TCB are the local and remotesocket numbers, the security and precedence of the connection, pointersto a user's send and receive buffers, pointers to the retransmit queueand to the current segment. Further, several variables that relate tothe send and receive sequence numbers of a transmission are stored inthe TCB.

TCP provides for many differing variables that may be used in order toaccomplish particular goals provided for by the protocol. For example,send sequence variables of TCP include:

SND_UNA send acknowledged. SND_NXT send next, a pointer that is used topoint to particular transmission or retransmission data. SND_WND sendwindow (32 bits) (31 bits is maximum remote offer window size). SND_MAXmaximum sequence number plus one, which is being sent to network (32bits). SND_WL1 records the sequence number of the last segment used toupdate SND_WND (32 bits). SND_WL2 records the acknowledged number of thelast segment used to update SND_WND (32 bits).

Within conventional TCP connections the SND_NXT command protocol isstored in conjunction with the SND_WND command in order to implement asegmentation window calculating process. The next transmission bitutilized by the segmentation unit is the SND_NXT command. Beforeconventional retransmission, the SND_NXT is shifted back before SND_MAX.

A check to see if a window should be updated is accomplished in theinstance that the SND_WND is an offset from the SND_UNA, wherein thevalue for SND_WND is updated when a segment contains new data and theSND_WL1 is before the start sequence value of the segment that updatesthe window at this point. In the instance that a segment does notcontain new data, then SND_WL1 will equal the start sequence number ofthe segment. Further, the segment will acknowledge the new data andSND_WL2 will precede the segment ACK sequence number of the segment.

The value for SND_WND is also updated in the instance that a segmentdoes not contain any new data and the segment does not acknowledge newdata in addition to the advertised send window being a larger SND_WNDthan the current SND_WND. The fore-mentioned parameters are utilized totrack the connection of a TCP retransmission queue in addition to theamount of data being transmitted within the connection. A furtherpurpose of the fore-mentioned parameters is to aid in the prevention ofold segment data from affecting the current send window since, asmentioned above, the SND_WND is an offset from the SND_UNA value.

Current TCP configurations that support thousands of connections causesystems that utilize the above-mentioned parameters to maintain largeretransmissions queues for the high number of connections. The presentinvention in addition to providing an independent connection forretransmission of data, does not utilize the SND_NXT protocol. In thepresent invention, a TOE transmission window is calculated based uponusing the SND_UNA value as a reference. Further, the present inventiondoes not store the values for SND_WND, SND_NXT, SND_WL1 and SND_WL2. Awindow is recalculated each time a TCP connection has data to transmit;thus, resulting in a significant saving of system memory.

A particular result of such a window-based flow control scheme is that asystem can fall victim to a condition known as the silly windowsyndrome. Silly window syndrome occurs when small amounts of data areexchanged across a connection instead of full-sized segments. Thesyndrome can be caused at either end of a TCP connection. For example,instead of waiting until a larger window could be advertised, a receivercan advertise small windows to a transmitter. Also, instead of waitingfor additional data to send a larger segment, a sender can transmitsmall amounts of data to a receiver.

A remedy for silly window syndrome is to have the receiver not advertisesmall windows. The normal algorithm is for the receiver not to advertisea larger window than it is currently advertising until the window can beincreased by either one full-sized segment or by one-half the receiver'sbuffer space, whichever is smaller. Accordingly, sender avoidance ofsilly window syndrome is accomplished by not transmitting a data packetunless a full-sized segment can be sent, at least one-half of themaximum sized window that the receiving party has ever advertised can besent, or all remaining data can be sent.

Aspects of the present invention provide a TCP transmission andretransmission connection to be the same, wherein they are identified byone identifier bit between the two connections. Additionally, thepresent invention can be implemented within systems that do not supportor maintain the SND_NXT command protocol or that do not use the SND_NXTparameter for retransmission purposes. Silly window condition is alsocontrolled within embodiments of the present invention. This aspect isaccomplished in conjunction with the masking of all negative windowresults by the forcing of the results of either condition to zero by thepresent invention. Lastly, outputs of the present invention are utilizedwithin application segmentation processing interfaces.

The present invention provides two channels for window calculationrequests in addition to having at least three stages of data processingfor embodiments of the present invention. These processing stagesinclude a parameter querying stage, an effective window calculatingstage, and an application transmit remain window calculation.

As illustrated in the flowchart 1400 of FIG. 14, when a send windowcalculator receives 1410 a request from an input channel, the calculatorreads 1420 all of the required parameters of a request before handingthe request off to a TCP transmit effective window calculator 1500stage. An exemplary TCP transmit effective window calculator 1500 thatcan be implemented in embodiments of the present invention isillustrated in FIG. 15. Still referring to FIG. 14, once the transmiteffective window calculator 1500 has processed the request, theresulting data is handed off to an effective window output register 1440and a TCP transmit application remain window calculator 1600 stage. Anexemplary TCP transmit application remain window calculator 1600 thatcan be implemented in embodiments of the present invention isillustrated in FIG. 16. Still referring to FIG. 14, the resultant fromthe TCP transmit application remain window calculator 1600 is thereaftertransmitted to an application remain window output register 1460.

As mentioned above, the TOE transmission window of the present inventionis calculated based upon using the SND_UNA value as a referenceparameter. Further, embodiments of the present invention have no need toreview the above-mentioned three conditions that are used to check if awindow should be updated. Accordingly, since the present invention hasno need to review the updating conditions, there is no need to store thevalues for the SND_WL1 And SND_WL2 parameters that are conventionallyused to assist in the above-mentioned window updating process. Thus,aspects of the present invention provide for the recalculation of theSND_WND every time the system performs a transmission or retransmissionwithout the use of large amounts of system memory.

The input parameter protocols for the TCP transmission window calculatorof FIG. 14 are displayed in table 1700 of FIG. 17. The resulting outputsfor the TCP transmission window calculator of FIG. 14 for two clockcycles, three clock cycles and 5 clock cycles are shown in tables 1800,1900, and 2000 of FIGS. 18, 19, and 20, respectively.

FIG. 21 is an illustration 2100 of the timing of the processes of thetransmission window calculator in regard to a system clock timing means.As mentioned above, negative transmission window results (i.e., sillywindow syndrome results) are automatically forced to zero withinembodiments of the present invention.

In view of the foregoing detailed description of preferred embodimentsof the present invention, it readily will be understood by those personsskilled in the art that the present invention is susceptible to broadutility and application. While various aspects have been described inthe context of a preferred embodiment, additional aspects, features, andmethodologies of the present invention will be readily discernabletherefrom. Many embodiments and adaptations of the present inventionother than those herein described, as well as many variations,modifications, and equivalent arrangements and methodologies, will beapparent from or reasonably suggested by the present invention and theforegoing description thereof, without departing from the substance orscope of the present invention. Furthermore, any sequence(s) and/ortemporal order of steps of various processes described and claimedherein are those considered to be the best mode contemplated forcarrying out the present invention. It should also be understood that,although steps of various processes may be shown and described as beingin a preferred sequence or temporal order, the steps of any suchprocesses are not limited to being carried out in any particularsequence or order, absent a specific indication of such to achieve aparticular intended result. In most cases, the steps of such processesmay be carried out in a variety of different sequences and orders, whilestill falling within the scope of the present inventions. In addition,some steps may be carried out simultaneously. Accordingly, while thepresent invention has been described herein in detail in relation topreferred embodiments, it is to be understood that this disclosure isonly illustrative and exemplary of the present invention and is mademerely for purposes of providing a full and enabling disclosure of theinvention. The foregoing disclosure is not intended nor is to beconstrued to limit the present invention or otherwise to exclude anysuch other embodiments, adaptations, variations, modifications andequivalent arrangements, the present invention being limited only by theclaims appended hereto and the equivalents thereof.

1. In a processor system for managing TCP communications, the processor system managing an original TCP connection with a TCP receiving system, the original TCP connection having transmission, and reception characteristics, a method of retransmission of a TCP segment to the TCP receiving system, comprising: determining that the TCP segment previously transmitted on the original TCP connection to the TCP receiving system needs to be retransmitted; establishing a selective context duplicated connection with the TCP receiving system, the selective context duplicated connection distinct from but having similar transmission characteristics as the original TCP connection; retransmitting the TCP segment to the TCP receiving system using the selective context duplicated connection rather than the original TCP connection; and maintaining the original TCP connection for on-going transmission of additional TCP segments to the TCP receiving system and for receipt of communications back from the TCP receiving system responsive to the TCP segment retransmitted on the selective context duplicated connection.
 2. The method of claim 1 wherein the step of determining is responsive to a timeout condition without receipt of an acknowledgement (ACK) from the TCP receiving system for the TCP segment previously transmitted by the processor system.
 3. The method of claim 2 wherein no further TCP segments are transmitted by the processor system until an acknowledgment of the retransmitted TCP segment is received back from the TCP receiving system.
 4. The method of claim 2 wherein the selective context duplicated connection is closed as soon as the TCP segment is retransmitted to the TCP receiving system.
 5. The method of claim 1 wherein the retransmission is a fast retransmission.
 6. The method of claim 1 wherein the original TCP connection is maintained for receipt of an acknowledgement (ACK) back from the TCP receiving system responsive to the TCP segments retransmitted on the original TCP connection.
 7. The method of claim 1 wherein the step of determining is responsive to receipt by the processor system of three duplicate acknowledgements (ACKs) from the TCP receiving system.
 8. The method of claim 7 wherein the TCP segment that needs to be retransmitted comprises the segment having a left edge sequence number corresponding to the sequence number of the three duplicate ACKs.
 9. The method of claim 1 wherein the reception characteristics of the selective context duplicated connection are disabled.
 10. The method of claim 1 wherein the reception characteristics of the original TCP connection are not used to define the selective context duplicated connection.
 11. The method of claim 1 wherein the selective context duplicated connection does not receive any communications back from the TCP receiving system.
 12. The method of claim 1 wherein the original TCP connection and the selective context duplicated connection are linked together by means of a TCP micro engine.
 13. The method of claim 1 wherein the step of determining comprises identifying a time out condition associated with the original TCP connection.
 14. The method of claim 13 wherein the TCP segment that needs to be retransmitted comprises the segment having a left edge sequence number corresponding to the sequence number of ACK last received from the TCP receiving system.
 15. The method of claim 1 further comprising the step of calculating a new RTO timer for the TCP segment that is retransmitted using the selective context duplicated connection and loading the value of the RTO timer to the original TCP connection.
 16. The method of claim 1 wherein the on-going transmission of additional TCP segments to the TCP receiving system using the original TCP connection occurs contemporaneously with the step of retransmitting the TCP segment to the TCP receiving system using the selective context duplicated connection.
 17. The method of claim 1 wherein the processor system includes a TCP state machine and a TCP micro engine.
 18. The method of claim 17 wherein the step of establishing the selective context duplicated connection with the TCP receiving system is performed by the TCP micro engine after receipt of a retransmission assistance request from the TCP state engine.
 19. The method of claim 17 wherein the selective context duplicated connection is closed by the TCP micro engine as soon as the TCP segment is retransmitted to the TCP receiving system by the TCP state machine.
 20. The method of claim 1 wherein the selective context duplicated connection is closed as soon as the TCP segment is retransmitted to the TCP receiving system.
 21. The method of claim 20 wherein, when the selective context duplicated connection is closed, the transmission characteristics of the selective context duplicated connection are reset and the selective context duplicated connection is made available to the processor system for retransmission use with another original TCP connection.
 22. The method of claim 1 wherein the sequence number of the last received ACK of the original TCP connection is used to define the left edge sequence number of the TCP segment to be retransmitted.
 23. The method of claim 1 further comprising the step of creating a data link list for the selective context duplicated connection with pointers pointing to data that needs to be retransmitted.
 24. The method of claim 23 wherein the data that needs to be retransmitted is included in the TCP segment that is retransmitted.
 25. The method of claim 1 further comprising, after determining that the TCP segment needs to be retransmitted, calculating a congestion window size for the original TCP connection.
 26. The method of claim 25 wherein the selective context duplicated connection is unaffected by the congestion window size of the original TCP connection.
 27. In a processor system for managing TCP communications, the processor system in electronic communication with a plurality of TCP receiving systems, a method of retransmission of a TCP segment to a designated one of the TCP receiving systems, comprising the steps of: managing a plurality of original TCP connections with the plurality of TCP receiving systems, each original TCP connection having respective socket, transmission, and reception characteristics; determining that the TCP segment previously transmitted to the designated one TCP receiving system on the original TCP connection with the designated one TCP receiving system needs to be retransmitted; establishing a selective context duplicated connection with the designated one TCP receiving system, the selective context duplicated connection distinct from but having similar transmission characteristics as the original TCP connection with the designated one TCP receiving system; retransmitting the TCP segment to the receiving TCP system using the selective context duplicated connection rather than the original TCP connection with the designated one TCP receiving system; and maintaining the original TCP connection with the designated one TCP receiving system for on-going transmission of additional TCP segments to the designated one receiving TCP system and for receipt of communications back from the designated one receiving TCP system responsive to the TCP segment retransmitted on the selective context duplicated connection.
 28. The method of claim 27 wherein the step of determining is responsive to a timeout condition without receipt of an acknowledgement (ACK) from the designated one of the TCP receiving systems for the TCP segment previously transmitted by the processor system.
 29. The method of claim 28 wherein no further TCP segments are transmitted to the designated one of the TCP receiving systems by the processor system until an acknowledgment of the retransmitted TCP segment is received back from the designated one of the TCP receiving systems.
 30. The method of claim 28 wherein the selective context duplicated connection is closed as soon as the TCP segment is retransmitted to the designated one of the TCP receiving systems.
 31. The method of claim 27 wherein the retransmission is a fast retransmission.
 32. The method of claim 27 wherein the original TCP connection with the designated one TCP receiving system is maintained for receipt of an acknowledgment (ACK) back from the designated one TCP receiving system responsive to the TCP segment retransmitted on the original TCP connection.
 33. The method of claim 27 wherein the step of determining is responsive to receipt by the processor system of three duplicate acknowledgements (ACKs) from the designated one TCP receiving system.
 34. The method of claim 33 wherein the TCP segment that needs to be retransmitted comprises the segment having a left edge sequence number corresponding to the sequence number of the three duplicate ACKs.
 35. The method of claim 27 wherein the reception characteristics of the selective context duplicated connection are disabled.
 36. The method of claim 27 wherein the reception characteristics of the selective context duplicated connection are not used to define the selective context duplicated connection.
 37. The method of claim 27 wherein the selective context duplicated connection does not receive any communications back from the designated one TCP receiving system.
 38. The method of claim 27 wherein the original TCP connection with the designated one TCP receiving system and the selective context duplicated connection are linked together by means of a TCP micro engine.
 39. The method of claim 27 wherein the step of determining comprises identifying a time out condition associated with the original TCP connection with the designated one TCP receiving system.
 40. The method of claim 39 wherein the TCP segment that needs to be retransmitted comprises the segment having a left edge sequence number corresponding to the sequence number of ACK last received from the designated one TCP receiving system.
 41. The method of claim 27 further comprising the step of calculating a new RTO timer for the TCP segment that is retransmitted by the selective context duplicated connection and loading the value of the RTO timer to the original TCP connection with the designated one TCP receiving system.
 42. The method of claim 27 wherein the on-going transmission of additional TCP segments to the designated one TCP receiving system using the original TCP connection with the designated one TCP receiving system occurs contemporaneously with the step of retransmitting the TCP segment to the designed one TCP receiving system using the selective context duplicated connection.
 43. The method of claim 27 wherein the processor system includes a TCP state machine and a TCP micro engine.
 44. The method of claim 43 wherein the step of establishing the selective context duplicated connection with the designed one TCP receiving system is performed by the TCP micro engine after receipt of a retransmission assistance request from the TCP state engine.
 45. The method of claim 43 wherein the selective context duplicated connection is closed by the TCP micro engine as soon as the TCP segment is retransmitted to the designated one TCP receiving system by the TCP state machine.
 46. The method of claim 27 wherein the selective context duplicated connection is closed as soon as the TCP segment is retransmitted to the designated one TCP receiving system.
 47. The method of claim 46 wherein, when the selective context duplicated connection is closed, the socket and transmission characteristics of the selective context duplicated connection are reset and the selective context duplicated connection is made available to the processor system for retransmission use with another original TCP connection.
 48. The method of claim 27 wherein the sequence number of the last received ACK of the original TCP connection with the designated one TCP receiving system is used to define the left edge sequence number of the TCP segment to be retransmitted.
 49. The method of claim 27 further comprising the step of creating a data link list for the selective context duplicated connection with pointers pointing to data that needs to be retransmitted.
 50. The method of claim 49 wherein the data that needs to be retransmitted is included in the TCP segment that is retransmitted.
 51. The method of claim 27 further comprising, after determining that the TCP segment needs to be retransmitted, calculating a congestion window size for the original TCP connection with the designated one TCP receiving system.
 52. The method of claim 51 wherein the selective context duplicated connection is unaffected by the congestion window size of the original TCP connection with the designated one TCP receiving system. 